Phosphorus Levels in the Great Lakes

Phosphorus levels remain an issue in the open watersFootnote [1] of three of the four Canadian Great Lakes. Phosphorus levels in the middle of Lake Superior and in the eastern basin of Lake Erie currently meet water quality objectives. Phosphorus levels in Lakes Huron and Ontario and in Georgian Bay are below water quality objectives, and above objectives in the western and central basins of Lake Erie.

Since 1970, phosphorus levels in the middle of Lakes Huron and Ontario, in Georgian Bay and in the eastern and western basins of Lake Erie have declined. Levels have not changed in Lake Superior or in the central basin of Lake Erie.

Status and trends of phosphorus levels in the open waters of the Canadian Great Lakes, 1970 to 2010


Long description

The map presents the results of the comparison of average spring total phosphorus concentrations in the Canadian Great Lakes (Superior, Huron and Georgian Bay Ontario and the western, central and eastern basins of Erie) to their phosphorus water quality objectives to determine the status of phosphorus concentrations in offshore waters in each lake. Phosphorus levels in the middle of Lake Superior and the eastern basin of Lake Erie currently meet target levels and are classified as good. In Lakes Huron and Ontario and Georgian Bay, phosphorus levels are below target concentrations and are given a caution classification. Levels are above water quality objectives in the western and central basins of Lake Erie. Since 1970, phosphorus levels have declined in all the lakes, except Lake Superior and the central basin of Lake Erie, where they have remained stable.

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How this indicator was calculated

Note: Status colours were determined by comparing average spring total phosphorus levels in water collected in the open water regions to water quality objectives for each lake set out in the 1978 Canada–U.S. Great Lakes Water Quality Agreement. The caution (yellow) designation used in this indicator is determined based on weight-of-evidence from several indicators describing other parts of the Lake Huron and Lake Ontario open-water food webs.
Source: Environment Canada (2012) Great Lakes Surveillance Program.

The water in the middle of each of the Great Lakes has naturally low levels of phosphorus. These lower phosphorus levels prevent algae from blooming to levels that cause problems. In the 1970s, symptoms of excessive algal growth caused by phosphorus levels due to human activity were evident in many regions of the Great Lakes. The 1978 Canada–U.S. Great Lakes Water Quality Agreement set objectives for open water phosphorus levels to keep algae from growing to nuisance levels. Upgrades to municipal wastewater treatment plants and limits on phosphorus levels in detergents started in the 1970s and were successful at reducing phosphorus levels, particularly in Lakes Ontario and Huron.

The accidental introduction of invasive zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels to the Great Lakes starting in the late 1980s has dramatically changed how and where phosphorus is available for plant growth in the lakes. These mussels are efficient at filtering particles and phosphorus out of water and converting phosphorus to a form that aquatic plants and algae can easily use to grow. In this way, nuisance aquatic plants and algae can thrive close to shore where most of the mussels live. Phosphorus in these areas does not flow out to the center of the lakes for use by food webs there. In Lake Huron, and to a lesser extent Lake Ontario, the lack of phosphorus in the open water is starting to limit the growth of algae which has impacts to the rest of the food web. Important fish, algae and plankton communities are showing clear signs of impairment more typical of very low phosphorus environments.

Environment Canada is working closely with its provincial and U.S. federal counterparts to more fully understand the relationships between phosphorus levels, invasive alien mussel species and nuisance algal growth.

Phosphorus is a key nutrient for plant growth in lakes. An oversupply of phosphorus can cause nuisance aquatic plants and algae grow to noxious levels resulting in changes to the types of fish that live in the lakes. Too little phosphorus can result in not enough plant growth which can result in a collapse of the fishery. Phosphorus from human activity enters the Great Lakes from municipal and industrial wastewaters, agricultural runoff and air pollution. Natural sources of phosphorus are rock weathering and the decay of dead plants and animals.

Related Indicators

Other information

This indicator is used to measure progress toward Target 3.4: Great Lakes – Contribute to the restoration and protection of the Great Lakes by developing and gaining bi-national acceptance of objectives for the management of nutrients in Lake Erie by 2016 and for the other Great Lakes as required of the Federal Sustainable Development Strategy 2013–2016.

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