About Osoyoos Lake
The name ‘Osoyoos’ comes from the First Nations (Syilx’tsn) word ‘suius (soo-yoos)’ meaning ‘place where the waters narrow’. The Okanagan Valley was heavily glaciated during the last Ice Age, which ended approximately 14,000 years ago. As the ice sheet retreated, the glacial meltwaters filled Osoyoos Lake and the other lakes in the Okanagan valley.
The lake system begins in Armstrong in the north Okanagan and is fed by the surrounding mountain snowpacks, down through a series of lakes connected by the Okanagan River: Kalamalka, Wood, Okanagan, Skaha and Vaseux Lake to Osoyoos Lake. Then it flows into the Okanogan River in Washington State and continues south via the Columbia River into the Pacific Ocean.
Osoyoos Lake is warmest freshwater lake in Canada. Lake temperatures can reach a high of 26° C in the summer months.
Osoyoos Lake is nearly 18 km long with 10.5 km of shoreline in Canada. The surface area of the lake is 2318 hectares, and it varies in depth from 8m to 64m. The elevation of Osoyoos Lake is 278m above sea level.
The water temperature and density change according to the seasons:
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Spring: As the ice melts and the surface water begins to warm, the increasing density of the warming water along with wind action causes this surface water to sink and mix with the deeper water. This is termed spring turnover.
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Summer: As the lake warms stratification occurs. The upper layer is a warm, well-mixed zone called the epilimnion. Below this is a transitional zone where temperatures rapidly change called the metalimnion. The thermocline is a horizontal plane within the metalimnion through the point of greatest water temperature change [5]. The metalimnion is very resistant to wind mixing. Beneath the metalimnion and extending to the lake bottom is the colder and relatively undisturbed hypolimnion.
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Autumn: as the surface water cools, it becomes denser and sinks to the lake bottom. Wind action causes mixing of the lake water. Eventually the entire lake reaches 4°C.
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Winter: As the surface water cools further, it becomes less dense and becomes layered on top of the denser 4°C water. Ice forms when the temperature reaches 0°C. Ice cover prevents the wind from mixing the water. This is termed winter stratification.
Osoyoos Lake is divided into three basins, known as the North Basin, Central Basin, and South Basin. Its deepest part is in the North Basin at 64 meters. It is about 24m deep near the U.S. Border.
The lake is an international waterway, straddling the 49th parallel. The water drains into the Okanogan River (yes, a different U.S. spelling of ‘Okanagan’) and then into the Columbia River system.
Osoyoos Lake is classed as “mesotrophic” meaning it is moderate in nutrients such as phosphates and nitrates and moderate in plant and algae growth. Osoyoos Lake has more phytoplankton (microscopic plants which float free in lakes) than most of the other Okanagan lakes. Water clarity measured using a Secchi disk ranges from 3-6 meters, depending upon season and location.
