acidity : A measure of the capacity of water to neutralize a strong base. In natural water this capacity is usually attributable to the presence of acids such as carbonic, nitric, sulphuric and organic acids or to acid cations like aluminum. See also pH. [Lat. acidus, sour.]

aeolian deposits : Material, predominantly sand and silt-sized particles, transported and deposited by wind. Sand dunes are examples of aeolian deposits. [Gk. Aeolus, god of winds.]

alkalinity : A measure of the capacity of water to neutralize a strong acid. In natural waters this capacity is attributable to basic ions such as bicarbonate, carbonate and hydroxyl ions as well as other ions often present in small concentrations such as silicates and borates. See also pH. [Fr. alcali, calcined ashes.]

algal bloom : A conspicuous concentration of phytoplankton, often concentrated at or near the surface. It is difficult to quantify what constitutes a "bloom". but a rough estimate places it as a chlorophyll a concentration over 30 µg/L. Blue-green algae are the predominant type of algae in most blooms in Alberta.

alluvial deposits : Sediments deposited by water but which may now be dry land. A delta is an example of an alluvial deposit. [Lat alluvius, wash.]

anion : See ion.

anoxic : Without oxygen. Anoxic water contains no measurable dissolved oxygen. Anoxic conditions often develop near the bottom of fertile lakes in summer and under ice in winter. [Gk. prefix a, without + Fr. oxygene.]

arability : A rating indicating the suitability of the soil for the production of crops. [Lat. arabilis, plough.]

area/capacity curve : A graph that shows the relationship between the depth, area and capacity (volume) of a lake or reservoir.

bathymetry : The measurements defining the size, depth and shape of a lake. [Gk. bathys, deep + metron, measure.]

bedrock : Continuous solid rock either exposed at the surface of the earth or overlain by a concealing cover of loose material such as that deposited by glaciers, water or wind.

benthic : Growing or living on or near the bottom of an aquatic system. Benthic invertebrates are small animals without backbones living on the bottom of a lake or river; for example clams and mayfly nymphs. [Gk. benthos, depth of the sea.]

benthos : The assemblage of organisms associated with the bottom sediments of aquatic systems. Benthos usually refers to the animals associated with the bottom sediments, but can also include plant and microbial communities. [Gk. benthos, depth of the sea.]

biomass: Weight of living matter. [Gk. bios, life - Lat. massa. a lump.]

blue-green algae : Algae of the Phylum Cyanophyta (also called Cyanobacteria), the most primitive group of algae. Blue-green algae are typified by cells without a true nucleus and with photosensitive pigments dispersed throughout the cell. Some species are capable of using nitrogen gas for metabolism, See also algal bloom. [Gk. cyano, blue + phyto, plant.]

Brunisol : Soils that develop on imperfectly-drained to well-drained sites on various types of parent materials. Brunisols develop under coniferous or deciduous forests.

buffer : A solution of weak acids and their dissolved salts which is able to greatly minimize changes in the hydrogen ion concentration (acidity). Most of the lakes in Alberta are well-buffered by bicarbonate ions and are therefore less susceptible to changes in pH by acid rain than the poorly buffered lakes on the Canadian shield,

buffering capacity : A measure of the resistance to acidification by acids or alkalinization by bases. See also buffer.

cation : See ion.

Chernozem : A soil group consisting of soils With a thick, nearly black surface horizon that is rich in organic matter from the decomposition of grasses and forbs. The surface horizon is underlain by a lighter-coloured transitional horizon which is above a zone of calcium carbonate accumulation. These soils occur in cool, subhumid to subarid climates under a vegetation of medium to tall grass prairie, and are usually excellent for growing crops.

chlorophyll a: One of the green pigments of plants. It is a photo-sensitive pigment that is essential for the conversion of inorganic carbon (for example, carbon dioxide) and water into organic carbon (for example, sugar). The concentration of chlorophyll a in water is an indicator of algal concentration. [Gk. chloros, green + phyllon, leaf.]

cobble: A stone that has been rounded by water, either by flowing water or wave action. Cobbles range in diameter from 7.5 to 25 cm. [ W. cob, lump.]

colour: In limnology, colour is a Measure of the humic material in water. It is measured by comparing filtered lake water to a mixture of platinum (Pt)-cobalt compounds, and is presented as units of Pt.

colluvium: A deposit of rock fragments and soil material that has accumulated at the base of steep slopes.

commercial fishing: The taking of fish to sell for profit. In Alberta, a licence is required for commercial fishing.

conductivity: See specific conductivity.

conduit: A pipe, tube or other channel for the conveyance of fluids. There is often a conduit to pass flow under or through major dams. [Lat. conducere, conductum, to conduct.]

control structure: A structure built to influence the natural flow of water. Dams, weirs and headgates are control structures.

coulee: A secondary valley of a main valley. Most coulees were created by water erosion during a period of high floods but they are now usually dry. Coulees are common in southern Alberta where they were created by meltwater during the retreat of the last glaciation.

creel survey: A census regarding species and numbers of fish caught by anglers over a period of time.

crenate: Indented, scalloped, notched. [Lat. crenatus, notched.]

crest: The highest part, as the highest part of a dam. [Lat. crista, a crest.]

Crown land: Land owned by the government, either federal (as in National Parks) or provincial.

Cryptophytes: Algae of the Phylum Cryptophyta. A small group of unicellular algae with two flagella emerging from a subapical pit. They usually have two chloroplasts and can he variously pigmented. [Gk. krupte. hide + phyto, plant.]

dam: A structure built across a waterway or valley to impound water. [Teut. dam.]

Denil II fishway: See fishway.

density: Mass of a substance in a unit volume, eg. g/cm3; or numbers per unit area or volume, for example, people per km2. [Lat. densitas, density.]

detritus: Tiny particles of material found in sediments or suspended in water. Organic detritus is derived from the decomposition of organisms: inorganic detritus is derived from the erosion of rocks and other mineral materials. Many text books on limnology restrict the meaning of detritus to include only organic detritus. [Lat. detritus, wearing down.]

diatoms: Algae of the Phylum Bacillariophyta. Microscopic unicellular algae occurring singly or grouped in colonies. Diatoms usually have thick, ornate siliceous cell walls. The cell walls form two distinct halves, like the top and bottom of a box, and they are marked with intricate, species specific patterns. [Lat. bacillus, stick + phyto, plant.] also [Gk. diatoms, alluding to the cells being connected in chains.]

dimictic lake: A lake that undergoes two periods of complete vertical mixing, usually in the spring and in the fall when the water temperature is the same from the surface to the bottom. During the summer, a dimictic lake is thermally stratified. [Gk. di, two + mictic, mix.]

dinoflagellates: Algae of the Phylum Pyrrhophyta. A diverse group of algae which are single cells with two flagella of different length. One flagellum is located in a transverse furrow which encircles the entire cell, the other is in a longitudinal furrow perpendicular to the first furrow along one half of the cell. Of all the algae, these are the fastest moving. [Gk. deinos, terrible + L. flagellum, whip.]

dissolved oxygen: Molecular oxygen in solution in a liquid. The amount of oxygen that will stay in solution in water is dependent on temperature, pressure and salinity. More oxygen can be dissolved in cold water than in warm water. For example, at sea level, water at 0°C is saturated with dissolved oxygen when the oxygen concentration is 14.2 mg/L; at 35°C water is saturated when the oxygen concentration is 7.0 mg/L. Saturation is also affected by pressure; as pressure (either atmospheric or hydrostatic) increases, the capacity to hold gases (like oxygen) increases. The capacity of saline water to hold dissolved oxygen is less than that of fresh water.

domestic fishery: The taking of large numbers of fish to form a significant portion of the diet for people or dogs. In Alberta, a licence is required; most licence-holders are native people or Metis on Metis settlement lands.

drainage basin: Defined for the Atlas as the land around a water body that contributes surface runoff to that body. See also watershed.

drawdown: The lowering of a reservoir or lake by controlled withdrawal.

dyke: A low bank of earth to prevent high water levels from flooding land. [ME. dik, dam.]

dystrophic lakes: Brown-water lakes with very low conductivity, low cation content and a very high humus content, often characterized by low plankton production. [Gk. dys, badly trophein, to nourish.]

ecoregion: An area characterized by a distinct climate as expressed by vegetation. Ecoregions in Alberta include Short Grass, Mixed Grass, Fescue Grass, Aspen Parkland, Montane, Subalpine, Alpine, Boreal Mixedwood, Boreal Uplands, Boreal Foothills, Boreal Northlands and Boreal Subarctic.

Ekman dredge: A metal traplike device used to sample the soft bottom sediment of a lake or river.

eluviation: The removal of soil material in suspension, or in solution within the soil, by the downward or lateral movement of water.

emergent macrophyte: Large, easily visible plants in which the lower part is submerged in water but the upper part extends above the surface. Bulrushes and cattails are emergent macrophytes.

epilimnion: The uppermost, warmest layer of a lake when a lake becomes thermally stratified in summer. The epilimnion lies above the metalimnion (thermocline). See also metalimnion, hypolimnion. [Gk. epi, on + limne, lake.]

euphotic zone: The upper layer of a water body as defined by light penetration; the upper limit is the water surface, the lower limit is the depth to which sufficient light for photosynthesis can penetrate. The euphotic zone is also called the trophogenic zone and occasionally the photic zone. The dark region below the euphotic zone is called the tropholytic zone. [Gk. eu, well - photo, light.]

eutrophic lakes: Lakes with a good supply of nutrients and hence a rich organic production of algae and macrophytes. In the Atlas, a lake is considered to be eutrophic if the peak chlorophyll a concentration exceeds 25 µg/L. [Gk. eu, well I trophein, to nourish.]

evaporation: The conversion of a liquid into a gas. The movement of molecules from a liquid into the air. [Lat. evaporo, evaporatum, out.]

fishway: A channel specially designed to facilitate upstream movement of fish in areas where their passage is otherwise blocked by high-velocity flows or vertical jumps. A step-pool fishway is a channel broken into small cascades with intervening resting pools. A Derail II fishway is a sloped channel with interior baffles to retard flow velocities to such a degree that upstream passage of fish is possible.

fluvial deposits: Sediments deposited by flowing water, including glacial meltwater. See also glaciofluvial deposits. [Lat. fluvius, river.]

freshwater lake: A lake with total dissolved solids concentration below 500 mg/L. See also saline lake.

fry: Newly hatched young fish, after the yolk has been used up and active feeding has commenced.

geodetic elevation: Altitude above sea level.

glacial till: Unstratified, poorly sorted material deposited directly by ice, consisting of clay, silt, sand, gravel and boulders intermingled in any proportion.

glaciofluvial deposits: Material moved by glaciers and subsequently sorted and deposited by streams or rivers flowing from the melting ice. The deposits are stratified and may occur in the form of outwash plains, deltas, eskers and kames. [Fr. glace, ice + Lat. fluvius, river.]

glaciolacustrine deposits: Material moved by glaciers and subsequently deposited in lakes formed by the melting of the ice sheet. [Fr. glace, ice - Lat. lacus, lake.]

Gleysols: Soils formed under imperfectly to very poorly drained conditions resulting in the reduction of iron and other elements. The soil has a grey mottled appearance with rusty brown iron stains or streaks.

golden-brown algae: Algae of the Phylum Chrysophyta, with dominant pigments chlorophyll a, xanthophyll and carotene. Species may be solitary or colonial; some have one or two flagella. [Gk. khrusos, gold + phyto, plant.]

green algae: Algae of the Phylum Chlorophyta. Pigments are primarily chlorophylls a and b. Some species have flagella, others are nonflagellate. Some species are solitary, others colonial or filamentous. [Gk. khloros, green - phyto, plant.]

groundwater: Water naturally flowing below the surface of the land. Surface groundwater is in the upper few metres of land; deep groundwater is below this. Groundwater is commonly a source of water for lakes whose basins are in glacial deposits and extend well below the water table.

hard water: Water containing high concentrations of alkaline earths, such as calcium and magnesium, derived from the drainage of calcareous deposits. Most of the lakes in Alberta are hardwater lakes. See also soft water.

hardness: An assessment of water quality based on the content of calcium and magnesium. Different scales are used in England, France. Germany and the United States. In the Atlas, hardness is expressed as an equivalent to 1 rag/L CaCO3 following a practice developed by early water supply engineers who wanted to standardize hardness and alkalinity to the same units.

headworks: The structures built to divert water from a river for irrigation. Most of the headworks in Alberta, such as those on the Bona River at Bassano and on the Highwood River at High River. are operated by the provincial government.

Humic Gleysols: Gleysolic soils which have an enriched layer of organic material that is usually made up of sedges or peat. Humic Gleysols develop in wet sedge meadows and in forested swamps.

hyper-eutrophic lakes: Lakes with very high concentrations of nutrients in the water. Hyper-eutrophic lakes are characterized by abundant plant growth, algal blooms, oxygen depletion and summer and winter fish kills. In the Atlas, a lake is considered to be hyper-eutrophic if the peak chlorophyll a concentration exceeds 75 µg/L. [Gk. hyper, excessive + eu, well + trophein, to nourish.]

hypolimnion: The deep cold layer of a lake lying below the metalimnion (thermocline) during the time a lake is thermally stratified. See also epilimnion, metalimnion. [Gk. hypo, under + limne, lake.]

ion: An electrically charged particle. Positively charged ions such as the hydrogen ion and metallic ions are called cations, negatively charged ions such as the hydroxyl ion and acid ions are called anions. [Gk. ion, going + kata, down + ana, up.]

limnology: The study of fresh water, especially the history, geology, biology, physics and chemistry of lakes. [Gk. lime, lake + logia, discourse.]

littoral zone: The portion of a lake where the bottom is within the euphoric zone and which supports rooted macrophyte growth. Sufficient light for photosynthesis reaches the bottom sediments in the littoral zone. [Lat. littus, shore.]

live storage volume: The amount of water in a reservoir that is available for controlled withdrawal. The volume of water in a reservoir between the full supply level and the lowest outlet structure.

Luvisol: A soil developed on a wide range of parent materials under mixed deciduous-coniferous forests in moderately well-drained to imperfectly drained sites.

macrophyte: Large, easily visible plants. Aquatic macrophytes include: emergent macrophytes such as cattails and bulrushes, submergent macrophytes such as pondweeds, floating-leaved macrophytes such as water lilies and free-floating macrophytes such as duckweed. [Gk. makros, great + phyton, plant.]

mesotrophic lakes: Lakes with moderate concentrations of nutrients in the water and hence support moderate production of algae and macrophytes. In the Atlas, a lake is considered to be mesotrophic if the peak chlorophyll aaconcentration is between 5 and 25 µg/L.

metalimnion: The layer of water in a thermally stratified lake between the epilimnion and the hypolimnion. The metalimnion is a narrow zone of rapid temperature change compared to the relatively small temperature changes within either the epilimnion or hypolimnion. See thermocline. See also epilimnion, hypolimnion. [Gk. meta, between + limne, lake.]

moraine: A deposit of unsorted, unstratified rock fragments transported by a glacier. Moraines are often hilly or hummocky. [Fr. moraine.]

muskeg: Wetland in boreal forest areas, typified by Sphagnum moss which accumulates to form peat, and black spruce. Muskeg is widespread in northern Alberta. Various estimates indicate that Canada may have more muskeg (1 300 000 km2) than any other country. [Algonquin muskeg. grassy bog.]

neotenic: A condition in which reproductively mature animals retain larvae characteristics. For example mature salamanders which retain external gills are said to be neotenic.

nutrient: A substance which nourishes to promote the growth or repair of organic bodies. The major plant nutrients include carbon, nitrogen, phosphorus and sulphur. [Lat. nutrire, nourish.]

offstream reservoir: An impoundment formed by building one or more dams across a relatively dry valley or coulee. Most of the water in the impoundment is brought to it by canal or pipeline from a river. Crawling Valley Reservoir, Milk River Ridge Reservoir and McGregor Lake are all offstream reservoirs.

oligotrophic lakes: Lakes with a low concentration of nutrients in the water and hence a low organic production of algae and plants. In the Atlas, a lake is considered to be oligotrophic if the peak chlorophyll a concentration is less than 5 µg/L. [Gk. oligos, small + trophein, to nourish.]

onstream reservoir: An impoundment of water formed by building a dam across a river or large stream which provides most of the water to the impoundment. Gleniffer Lake, Ghost Reservoir and Glenmore Reservoir are onstream reservoirs in Alberta.

Organic soils: Soils in areas of extremely poor drainage and containing a large fraction of plant and animal residues at various stages of decomposition.

peat: Unconsolidated soil material consisting largely of decomposed or partially decomposed organic material accumulated under conditions of excessive moisture. Sphagnum moss is often a major component of peat.

pelagial zone: The open water zone of a lake or sea; the zone of a lake or sea far from shore. [Gk. pelagos, the high sea.]

penstock: A tube or conduit for conducting water, usually directing flow to electrical generators.

periphyton: Algae growing attached to something. The following communities of periphyton can be differentiated: epipelic algae grow on fine sediments, epilithic algae grog: on rocks, epiphytic algae grow on macrophytes, epizooic algae grow on animals, and episammic algae grow on or between grains of sand. [Gk. peri, around + phyto, plant.]

pH: The negative logarithm of the hydrogen ion activity (approximate concentration) expressed in gram equivalents. On a scale of 1 to 14, solutions with a pH less than 7 are acidic, those with a pH above 7 are basic; a pH of 7 is considered to be neutral.

photic zone: See euphotic zone. [Gk. photo, light.]

photosynthesis: The process in which light energy in the presence of the chlorophyll pigment. water and adequate nutrients, is used to produce organic carbon or solid plant material from inorganic carbon. [Gk. photos, light + syn, together + tithenai, to place.]

phytobenthos: Algae or rooted plants living on the bottom of a lake or river; the plant component of the benthos. [Gk. phylo, plant - benthos, depth of the sea.]

phytoplankton: The plant portion of the plankton. See also plankton. [Gk. phyto, plant + planktos, wandering.]

plankton: The free-floating or suspended community of tiny plants (phytoplankton) and animals (zooplankton). [Gk. planktos, wandering.]

precipitation of water: Water which falls from the sky as rain, snow, or hail. [Lat. praecipitium, falling headlong.]

precipitation in a solution: The formation and settling of minerals or salts from a supersaturated solution.

profundal zone: The deep region of a water body below the limit where light is sufficient for plant growth. [Lat. profundus, deep.]

proglacial lake: A lake lying at or near the foot of a glacier. [Lat. pro, in front + Fr. glace, ice.]

Regosol: Soils that occur where natural disturbance has inhibited the development of soil horizons. These soils are found in well-drained to imperfectly drained sites; they are common near river beds, on colluvium, on steep and active erosional slopes, and on shallow parent material over bedrock in the mountains.

regulated lake: A lake with a surface elevation that is controlled to some extent by a weir or diversion.

residence time: The average length of time that water stays in a reservoir or lake, also called the hydraulic residence time. It is usually calculated by dividing the volume of the waterbody by the average annual out flow. In the Atlas, the estimate of residence time usually did not consider groundwater inflow or outflow, because they have not been measured in most lakes.

riparian: Pertaining to the bank of a body of water. [Lat. ripa, a bank.]

runoff: The water reaching a lake, stream or ocean after flow over land or through the surficial layers of the land. Surface runoff includes streamflow, whereas subsurface runoff moves laterally in the upper soil horizons and groundwater flows laterally deep in the ground.

saline lake: Saline means salty; a saline lake has a higher concentration of salts than a freshwater lake. In the Atlas, a freshwater lake is defined as one with a total dissolved solids (TDS) concentration of less than 500 mg/L A slightly saline lake has a TDS concentration between 500 and 1 0OO mg/L, a moderately saline lake has a TDS concentration between 1 0OO and 5 000 mg/L, and a highly saline lake has a TDS concentration over 5 000 mg/ L. See also total dissolved solids. [Lat. sal, salt.]

salinity: The ionic composition of water, expressed as mg/L. The concentration of four major cations (calcium, magnesium, scdiurn, and potassium) and four major anions (bicarbonate, carbonate. sulphate, and chloride) collectively approximate salinity in lakes in the Atlas. The relative salinity of lakes is usually determined by comparing their concentration of total dissolved solids. [Lat. sal, salt.]

salts: A general term for chemical which. when dissolved in water, separate into negatively and positively charged ions.

Secchi depth: The depth in water to which a Secchi disc (a 20-cm diameter disc with alternating black and white quadrants) can be seen from the surface. Secchi depth is an easy measurement of water transparency.

sediment: Material that is too dense to remain suspended and settles to the bottom of a liquid, The sediment usually originates from the remains of phytoplankton, zooplankton and other aquatic organisms, from erosion of surrounding lands, or from chemical precipitation of dissolved minerals. [Lat. sedimentum, from sedeo, to settle.]

sheet-pile weir: A control structure built of pilings driven into the ground to support sheets of steel to hold back water. Sheet-pile weirs have been built in several Alberta lakes to raise the water level slightly (usually less than 1 m) or to control outflow from the lake.

shore: The land immediately upslope from the surface of a lake or reservoir.

soft water: Water containing low concentrations of calcium and magnesium. Soft water lakes are common on the Precambrian Shield in northern Saskatchewan, Manitoba, Ontario and Quebec; they are not common in Alberta. See also hard water.

Solonetzic: An order of moderately well-drained to imperfectly drained soils developed on saline parent material in cool subhumid to subarid climates under grassland vegetation. Solonetzic soils usually occur in association with Chernozemic soils.

specific conductivity: A measure of the ease of passing an electrical current through a liquid from one 1 cm2 electrode to another 1 cm2 electrode, 1 cm apart, at 25°C or 20°C. Specific conductivity increases with increased salinity. The units are µS/cm which is equivalent to µmhos/cm (reciprocal of ohms).

spillway: A channel that conducts water past a dam. A spillway routinely passes flow whereas an emergency spillway is used only when the water level of a reservoir exceeds the full supply level.

step-pool fishway: See fishway.

stratified: Separated into layers. In stratified lakes, there may be mixing within a layer but little mixing occurs between layers. Layers have different densities. which may he determined either by temperature and/or salinity. See also epilimnion. hypolimnion, thermocline, thermally stratified.

sublittoral zone: The zone of the lake bottom that is a transition between the littoral zone and the profundal zone. Light is sufficient in the littoral zone to support abundant rooted plant growth; there is insufficient light in the profundal zone for any plant growth. The sublilloral zone is occupied by scattered plants that may survive a short time and by benthic algae (mostly blue-green) and photosynthetic bacteria. [Lat. sub, below + littus, shore.]

submergent macrophytes: Large aquatic plants which grow below the surface of the water although the flowers may extend above the surface. Pondweeds and northern water milfoil are submergent macrophytes.

summerkill: An event when large numbers of animals, including fish, die from critically low dissolved oxygen concentrations. When an unusually large population of algae dies, the subsequent decomposition consumes oxygen and summerkill may result. Summerkill of fish also occasionally results from the water temperature rising to near-lethal levels. combined with high concentrations of ammonia released as a consequence of decomposition of plant material.

surficial deposits: Material such as clays and gravels overlying bedrock. Glacial till is a surficial deposit.

thermocline: The depth within the metalimnion of a thermally stratified lake where the temperature gradient is greatest and exceeds a change of 1°C per metre of depth. See also metalimnion, thermally stratified. [Gk. therme, heat + kleinen, to slope.]

thermally stratified: Divided into layers with different density due to temperature differences. In a thermally stratified lake in summer, warmer water in the epilimnion floats above denser, colder water in the hypolimnion: the zone of rapid temperature change is the metalimnion.

topography: The physical features of a landscape especially its relief and slope. [Gk. topos. place + graphos, written.]

total dissolved solids: The total inorganic and organic materials dissolved in water. The total dissolved solids in water can be determined after water is filtered through a 0.45 µm filter and evaporated to dryness at 103°C to 105°C, or it can be estimated from concentrations of major ions (calculated).

trophic state: The degree of fertility of a lake. Factors used to assess the trophic state of a lake include chlorophyll a, dissolved oxygen and phosphorus concentrations. algal biomass, Secchi depth and macrophyte biomass. See also hyper-eutrophic lakes, eutrophic lakes, mesotrophic lakes. oligotrophic lakes, dystrophic lakes.[Gk. trophe, nourishment.]

trophogenic zone: See euphotic zone. [Gk. trophe, nourishment + gennan, to produce.]

tropholytic zone: See eupholic zone. [Gk. trophe, nourishment and lyo, to dissolve.]

turbid: Opaque with suspended matter. Water with conspicious amounts of mud, silt or algae suspended in it is said to be turbid. [Lat. turbidus, disturbed.]

water column: A vertical segment of a lake that extends from the surface to the bottom.

watershed: The land contributing surface runoff to a stream or lake; a drainage basin.

water table: The upper limit of the soil or underlying rock material that is wholly saturated with water.

weir: A control structure built across a stream or lake outlet to raise the water level a small amount. [OE. waer, a fence.]

winterkill: An event when large numbers of animals, including fish, die from critically low oxygen concentrations under the ice. In many shallow Alberta lakes, the decay of algal and plant material under ice consumes so much oxygen that winterkills occur.

zooplankton: The animal portion of the plankton. See also plankton. [Gk. zoon, animal + planktos, wandering.]