Algae blooms are the uncontrolled growth of one or more species of algae, which may result from excessive nutrient loading in combination with adequate light, temperature, and other environmental factors.

Hundreds of thousands of salmon excreting in the confined area of a farm can cause a localized level of nutrient loading that may not be completely absorbed by the surrounding environment; hence, nutrient loading from salmon farms may be linked to algal blooms

Similarly, climatic events and ocean currents can cause off shore pockets of nutrient rich water “well up” in near shore areas and cause similar blooms.

Algae blooms are a widespread problem for salmon farmers up and down the entire BC coast, particularly during late summer and early fall. This is when high concentrations of an algae known as Heterosigma akashiwo tends to bloom. It is transported by wind or water currents into salmon net pens and, at high enough densities can kill the fish in a short period of time. 

In September 2007, Marine Harvest Canada had approximately 260 tonnes of farmed Atlantic salmon die by algae blooms at a farm in Klemtu, BC.

Closed containment systems could prevent nutrient loading in the ecosystem by recovering or treating waste. Learn more about the closed containment solution.