Lac St. Cyr

Basic Info
Map Sheets73E/14
Lat / Long53.9000000, -111.2000000
53°53'N, 111°12'W
Area2.46 km2
Max depth21 m
Mean depth5.1 m
Dr. Basin Area28.1 km2
Dam, WeirNone
Drainage BasinNorth Saskatchewan River Basin
Camp GroundNone
Boat LaunchHand/Small Boat
Sport FishYellow Perch, Northern Pike
Trophic StatusMesotrophic
TP xNorth: 29
East: 26 µg/L
CHLORO xNorth: 5.8
East: 6.6 µg/L
TDS xNorth: 189
East: 189 mg/L
Photo credit: E. Stockerl and R. Kent


Lac St. Cyr is a small, attractive lake located in the County of St. Paul, southeast of the town of St. Paul. To reach the lake, take Secondary Road 881 south from St. Paul for 10.5 km, then turn east on Secondary Road 646 for 2 km to a dirt track leading to the southwest side of the lake (FIGURE 1). There is a county-owned launching area for small boats there (FIGURE 2), but no other recreational facilities. A former resort on the southeastern bay was a private retreat centre in 1989, and not available to the public.

Because it is close to town, Lac St. Cyr is popular with residents of St. Paul. There are about 18 cottages in a subdivision of 28 lots on the south shore. Fishing for yellow perch and northern pike can be quite good at times. There are no special sport fishing regulations for the lake, but provincial limits and regulations apply (Alta. For. Ld. Wild. 1989). Sand is present around the shoreline and the clear water encourages boating and swimming. The best beach is at the private retreat. There are no specific boating regulations for Lac St. Cyr, but general federal regulations apply (Alta. For. Ld. Wild. 1988).

The lake has been used as a water supply for the town of St. Paul since 1951. By 1978, the lake level had declined about 3 m from levels in the 1950s. Concern expressed by the town and by recreational users prompted Alberta Environment to construct a diversion from the North Saskatchewan River to supplement the lake volume. Pumping commenced in 1978. It is restricted to fall and early winter, because studies suggested that the impact on the water quality of the lake would be least during those seasons. As of 1986, there had been little significant change in water quality in Lac St. Cyr as a result of the diversion and the water level had increased. Although blue-green algae tint the water green in July and August, the water is usually quite clear. Aquatic vegetation is prolific in shallow areas. The deep north basin tends to have somewhat better water quality than the shallow western and eastern basins.

Drainage Basin Characteristics

The drainage basin is about 11 times larger than the area of the lake (Tables 1, 2). About one-third of the land has been cleared for agriculture; barley, oats, wheat, canola, field peas and hay are grown in the area (Piquette 1988). The dominant natural vegetation - trembling aspen, balsam poplar, white spruce and willow - is typical of the dry mixedwood forest. Balsam poplar is prevalent along the backshore and on the largest island.

The terrain around the lake is gently to strongly rolling (6 to 30% slope). The dominant soils in the watershed are Gray Luvisols developed on fine loamy glacial till and coarse loamy glaciofluvial deposits. Soils found in minor amounts (less than 20% of the area) are Dark Gray Luvisols or Dark Gray Chernozemics developed on fine loamy till. The Gray soils have low natural fertility, whereas the Dark Gray soils are more fertile (Brierley et al. 1988).

There are no major natural surface inflows to the lake, and the outlet, at an elevation of 647.7 m, has not flowed for many years (Doell and Tamjeedi 1978). At one time, the outlet drained toward Siler Lake and then to the North Saskatchewan River.

Lake Basin Characteristics

Lac St. Cyr is a small lake with an irregular outline (FIGURE 2). The northern basin is the deepest (maximum depth of 21 m, TABLE 2), and the bottom slopes steeply toward the deep area. The western portion of the lake is the shallowest; much of it is littoral and aquatic vegetation is abundant. The eastern bay slopes gently to a maximum depth of about 8 m. The islands in the lake are very low and all but the largest would be inundated with a small rise in lake level.

The highest water level recorded in Lac St. Cyr was 647.06 m in 1959 and the lowest was 644.21 m in 1978 (FIGURE 3). The decline over these years amounts to 2.85 m. To supplement the lake, Alberta Environment has operated a diversion from the North Saskatchewan River since 1978. Between 1978 and 1985, the average annual diversion volume was 0.987 x 106 m3 and the Town of St. Paul withdrew an annual average volume of 0.882 x 106 m3 (Alta. Envir. n.d.[b]). The lake's water level has increased since the diversion began. The establishment of an optimum level was based on a compromise among property holders on the lake (Doell and Tamjeedi 1978). The quantity pumped is designed to increase the water level to the optimum level and to maintain this level by replacing the portion removed as water supply.

Much of the bottom sediment in the shallower areas is sandy, but silt and organic material are present along the shore in the deep north basin; aquatic plant growth extended to a depth of 4 m in 1984 (Stocked and Kent 1984). This colonized area represents 43% of the area of the lake (FIGURE 4).

Water Quality

The water quality of Lac St. Cyr was studied by Alberta Environment from 1977 to 1980 and in 1983 and 1986 to determine the effect of the diversion from the North Saskatchewan River (Alta. Envir. n.d.[a]; Reynoldson 1977; Mitchell 1987).

As a result of the diversion, the ionic composition of the lake has shifted to resemble that of river water. The total salinity of the river and lake were similar before 1978, but now calcium and sulphate are significantly higher in the lake and potassium and magnesium have decreased (TABLE 3). Bicarbonate and calcium are the dominant ions.

The deep north basin thermally stratifies between May and September (FIGURE 5), whereas the shallower east basin is only weakly thermally stratified in midsummer. The remainder of the lake mixes on windy days all summer. The north basin does not mix completely in spring most years, so the anoxia that builds up over winter in the bottom half of the water column remains until fall turnover, when complete or partial mixing occurs (FIGURE 6). Anoxia develops at the bottom during summer stratification in other parts of the lake, but the bottom water is reoxygenated during windy periods. Fish kills as a result of a lack of oxygen are unlikely in summer or winter because of the lake's depth.

The water in Lac St. Cyr is often very transparent. One of the deepest Secchi depths recorded from Alberta lakes was measured in this lake (11 m, June 1983). The lake has low levels of phosphorus and chlorophyll a (TABLE 4); it is classified as mesotrophic. Average chlorophyll a data for the open-water season for pre- and post-diversion periods are presented in TABLE 5. There is little difference among average chlorophyll a values for any of these years. Up to the end of 1986, the diversion had had no obvious effect on water quality in the lake, even though phosphorus levels in the river water are about 4 times higher than those in the lake water and the annual external phosphorus supply has increased by 25% (TABLE 6).

The patterns of chlorophyll a and phosphorus fluctuations over the summer are typical of many lakes in Alberta (FIGURE 7). In the north basin, chlorophyll a levels remain low until fall, when nutrient-rich water from the hypolimnion mixes into the upper water and stimulates algal growth. Mixing usually occurs earlier in the shallow east basin than in the north basin. In some years, chlorophyll a concentrations peaked in August in the east basin, which is typical of shallow lakes that mix intermittently.

Biological Characteristics


The phytoplankton was studied by Alberta Environment in 1983 as part of the diversion impact assessment (Alta. Envir. n.d.[a]). The total biomass is low compared to that in more productive lakes. Blue-green algae are dominant in summer (TABLE 7) but they rarely have become so abundant that the population would be called a "bloom". There was little difference in biomass and composition between the two basins.

Macrophytes were surveyed by Alberta Environment in 1978 before the start-up of the diversion, and again in 1984 (Stocked and Kent 1984; Mitchell 1987). Northern watermilfoil (Myriophyllum exalbescens) was dominant in 1978, whereas large-sheath pondweed (Potamogeton vaginatus) and stonewort (Chara sp.) were the dominant species in 1984 (FIGURE 8). Populations were very dense in shallow areas in the southern and western parts of the lake during both survey years. Filamentous algal mats associated with stands of Potamogeton spp. were prevalent in 1978 and in 1984, but appeared to be more abundant in 1984.


There are no data available on the zooplankton of Lac St. Cyr.

Benthic invertebrates were collected with an Ekman dredge in October 1976 from each basin of the lake (Alta. Envir. n.d.[a]; Reynoldson 1977). Flatworms (Dugesia tigrina) were dominant in the shallowest areas near shore; leeches (Nephelopsis obscura, Glossiphonia complanata and Helobdella stagnalis) and caddis fly larvae (Trichoptera: Leptocella sp.) were also abundant. In the deepest area of the north basin, the phantom midge larva (Chaoborinae: Chaoborus sp.) was dominant, but midge larvae (Chironominae and Tanypodinae) and aquatic earthworms (Oligochaeta) were common as well. Chaoborus sp. was also very abundant in the deeper water of the other basins.


Little is known of the fish and fishery of Lac St. Cyr. Yellow perch and northern pike are present in the lake, and "pickerel" (probably walleye) were stocked as eggs in May 1959. No significant walleye population developed from this stocking (Alta. For. Ld. Wild. n.d.). The lake was reported to be used fairly heavily by pleasure boaters and casual anglers in 1970 (Smith and McMillan 1970). Large yellow perch are the main target for the local sport fishery. The lake is not fished commercially.


Lac St. Cyr is not particularly valuable for wildlife; waterfowl production is low compared to that on surrounding pothole lakes (Doell and Tamjeedi 1978). No documentation of species nesting on the lake exists.

P.A. Mitchell


Alberta Environment. n.d.[a]. Envir. Assess. Div., Envir. Qlty. Monit. Br. Unpubl. data, Edmonton.

-----. n.d.[b]. Tech. Serv. Div., Hydrol. Br. Unpubl. data, Edmonton. n.d.[c]. Tech. Serv. Div., Surv. Br. Unpubl. data, Edmonton.

Alberta Forestry, Lands and Wildlife. n.d. Fish Wild. Div. Unpubl. data, Edmonton.

-----. 1988. Boating in Alberta. Fish Wild. Div., Edmonton.

-----. 1989. Guide to sportfishing. Fish Wild. Div., Edmonton.

Alberta Research Council. 1972. Geological map of Alberta. Nat. Resour. Div., Alta. Geol. Surv., Edmonton.

Brierley, A., W.L. Nikiforuk and L.A. Andriashek. 1988. Soil survey of the County of St. Paul. Interim maps. Alta. Res. Counc., Edmonton.

Doell, B.C. and A. Tamjeedi. 1978. Lac St. Cyr stabilization study. Alta. Envir., Plan. Div., Edmonton.

Energy, Mines and Resources Canada. 1976. National topographic series 1:50000 73E/14 (1976). Surv. Map. Br., Ottawa.

Environment Canada. 1982. Canadian climate normals, Vol. 7: Bright sunshine (1951-1980). Prep. by Atm. Envir. Serv. Supply Serv. Can., Ottawa.

Mitchell, P.A. 1987. Lac St. Cyr: The impact of river diversion on water quality. Alta. Envir., Poll. Contr. Div., Water Qlty. Contr. Br., Edmonton.

Piquette, K. 1988. Alta. Agric., St. Paul. Pers. comm.

Reynoldson, T. 1977. A preliminary assessment of the effects of diversion on Lac St. Cyr. Alta. Envir., Poll. Contr. Div., Water Qlty. Contr. Br., Edmonton.

Smith, A. and B. McMillan. 1970. Lac St. Cyr. Alta. Ld. For., Fish Wild. Div. Unpubl. rep., Edmonton.

Stocked, E.C. and R. L. Kent. 1984. Lac St. Cyr aquatic macrophyte survey 1984. Prep. for Alta. Envir., Poll. Contr. Div., Water Qlty. Contr. Br., Edmonton.

Strong, W.L. and K.R. Leggat. 1981. Ecoregions of Alberta. Alta. En. Nat. Resour., Resour. Eval. Plan. Div., Edmonton.

Wyatt, F.A., J.D. Newton, W.E. Bowser and W. Odynsky. 1944. Soil survey of Wainwright-Vermilion sheet. Alta. Soil Surv. Rep. No. 13, Univ. Alta. Bull. No. 42. Univ. Alta., Edmonton.