The Winnipeg River Basin

The Winnipeg River drainage basin is the most significant of Lake Winnipeg's sub-basins, contributing 45% of total inflow, 25% of nitrogen loading, and 12% of phosphorous loading. In turn, the Lake of the Woods sub-basin, straddling the border between Ontario and Minnesota, is the most important of the Winnipeg River's drainage areas, contributing half of its flow.

The Minnesota Pollution Control Agency (MPCA) recently completed a multi-year assessment of the nutrient and algae conditions on the Lake of the Woods. The results of the assessment may lead to the MPCA adding the lake to its draft list of "impaired" waters. Similarly, on the Canadian side of the border, the occurrence of algal blooms on the lake has lead the Lake of the Woods Water Sustainability Foundation to initiate a nutrient budget study of the lake.

In addition to agricultural runoff, cottage development is among the suspected sources of Lake of the Woods' nutrient loading. One of the adverse impacts of nutrient loading is the production of toxic microcystin by the blue-green algae present in the lake in elevated numbers. Last summer it was found that microcystin was present in the lake at levels that posed a high risk for recreational use.

Mercury contamination is also a concern on Lake of the Woods. The heavy metal naturally occurs in the bedrock beneath the lake. However, the Minnesota Pollution Control Agency reports that most mercury entering lakes in the region comes from the atmosphere, as air-borne emissions from coal-fired power plants, mining sites, and manufacturing facilities. In light of the elevated levels of mercury found in fish in Lake of the Woods, The Guide to Eating Ontario Sport Fish recommends limits on the size and number of fish consumed for a number of species. More stringent limits are recommended for children and women of childbearing age.

Thanks to the Lake of the Woods Property Owners Association for use of this article by J.J. Ross.