The Shuswap Watershed Council (SWC) says the large algae bloom in Shuswap Lake is the result of various factors which amount to a “perfect storm scenario.”
Program manager Erin Viera said algae is a natural part of Shuswap Lake’s aquatic ecosystem but changes in conditions can cause more prominent blooms. She said blooms are common when sunlight increases and runoff down creeks and rivers brings a fresh supply of nutrients into the lake.
Referring to a recent SWC study on the origins of the nutrients that are brought into Shuswap Lake by the Shuswap and Salmon Rivers, Viera noted that most of the nutrients from the rivers come from the valley bottoms. Agriculture, housing and commercial development in the watershed all affect the nutrient levels in the river.
Viera said that as 2020 has been a very wet year, the Salmon River has been running higher than usual for months. The soil in the valley bottoms has also been saturated by rain causing nutrients to be flushed out of the soil into the river and down stream to Shuswap Lake. As the nutrients — particularly phosphorous — from the river settled in Salmon Arm bay, favourable conditions for the growth of large amounts of algae were created.
She said a similar effect was probably created in Tappen Creek and White Creek, which also flow into Salmon Arm Bay.
Viera added that the heavy rains this year might’ve contributed to the release of “legacy phosphorous” which is stored in soil for years or even decades. Septic systems near the lake and the Salmon Arm wastewater treatment plant are also sources of nutrients, but Viera said water quality monitoring has shown that they are smaller sources than the Salmon River.
Nutrient increases lead to algae blooms in Salmon Arm Bay more than other parts of the lake because its shallow depth causes it to warm up more quickly. It is also relatively stagnant, and conditions are favourable to algae growth if the water isn’t mixed by currents or windstorms.
Water quality monitoring is also ongoing on the algae bloom itself. Viera said authorities are ensuring the bloom doesn’t pose a safety risk to swimmers or beach goers. If it becomes hazardous, notices will be posted at affected sites.