Nutrient Loading and Algal Blooms

Photo: algal bloom © Michel Starr, Institut Maurice-Lamontagne, DFO

Nutrient loading

Nitrogen and phosphorus levels in water bodies

Percentage of sites with increasing, decreasing, and stable trends between 1990 and 2006
Two pie charts showing the percentage of sites with increasing, decreasing and stable trends in nitrogen and phosphorus. Click for graphic description (new window).
Note: these are the results of 83 sites monitored for nitrogen and 76 sites monitored for phosphorus through federal and provincial water quality monitoring programs.
Source: adapted from Environment Canada, 20102

  Photo: Skaha lake © Epp
  Skaha Lake, B.C.

Reductions in nutrient loading in Skaha Lake, B.C.

Micrograms/litre of phosphorus, chlorophyll a and milligrams/litre of dissolved oxygen, 1968 to 2008
Graph: reductions in nutrient loading in Skaha Lake, B.C. Click for graphic description (new window).
Note: left axis is phosphorus and chlorophll a; right axis is dissolved oxygen.
Source: updated from Jensen and Epp, 200226


The Okanagan River Basin drains through a chain of lakes in the southern interior of B.C., ultimately leading to the Columbia River. Since the early 1970s, controls have been introduced to reduce nutrient pollution in the region, with the most significant reductions made in agricultural and sewage treatment inputs. This has resulted in significant declines in phytoplankton (measured as chlorophyll a) and phosphorous and an increase in dissolved oxygen. Skaha Lake is one of the lakes in the Okanagan where nutrient loading has been reduced.