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What is the Problem?

Toxic and nuisance algal bloom occurrences in Lake Erie have increased over the past decade. The blooms threaten drinking water quality, increase costs associated with treatment needs, and occasionally force closures of treatment plants. They clog industrial water intake systems, adversely impact commercial and recreational fishing activities and other recreational pursuits, and degrade fish and wildlife habitat and populations.

Excessive algal blooms in the 1960s and 1970s were a major driver for the signing of the first Agreement in 1972. In that first Agreement, the Governments of Canada and the U.S. agreed to reduce phosphorus loads to Lake Erie by more than 50 percent (from 29,000 to 14,600 metric tons per year). In the 1978 Agreement, the two countries agreed to a further reduction of phosphorus loads to Lake Erie to 11,000 metric tons per year. Regulation of phosphorus concentrations in detergents, investing in sewage treatment, and developing and implementing best management practices on agriculture lands successfully achieve those targets. With the achievement of phosphorus load targets, algal bloom development in Lake Erie decreased significantly throughout the 1980s. However, in the 1990s, despite ongoing efforts to limit phosphorus discharges to Lake Erie, toxic and nuisance algal blooms began increasing.

Annual total phosphorus load to Lake Erie.
From Scavia et al. 2014. Assessing and addressing the re-eutrophication of Lake Erie: Central basin hypoxia.
Journal of Great Lakes Research
40: 226-246.

Three key issues need to be addressed: algal toxins, the size of the low-oxygen (hypoxic) area that is created when algae die and decompose, and the presence of Cladophora.

In 2011, concentrations of the algal toxin microcystin in the open waters of the Western Basin of Lake Erie were 50 times higher than the World Health Organization limit for safe body contact, and 1,200 times higher than the limit for safe drinking water. In August 2014, algal toxins forced closure of the Toledo, Ohio, drinking water treatment plant and private water users on Pelee Island, Ontario, were warned not to bathe in or drink Lake Erie water. The incident affected more than 500,000 people.

Since the early 2000s, the hypoxic (low-oxygen) area in the Central Basin of Lake Erie has increased to about 4500 km2, on average, with the largest hypoxic event of 8,800 km2 occurring in 2012. Hypoxic conditions can affect the growth and survival of fish species. In 2012, hypoxic conditions were responsible for tens of thousands of dead fish washing up on a 40 kilometre stretch of shoreline between Erieau and Port Stanley, Ontario.

Cladophora is a filamentous green algae that grows on hard substrates in all of the Great Lakes. Beginning in the early 2000s, mats of Cladophora in the Eastern Basin of Lake Erie have caused beach fouling, undesirable odours from decomposing Cladophora, clogged industrial intakes and degraded fish habitat.

The GLWQA Nutrients Annex Subcommittee has suggested that the Lake Erie algae problem can best be described in relation to the three main basins of the Lake:

  • The Western Basin is very shallow with an average depth of 7.4 meters (24 feet) and a maximum depth of 19 meters (62 feet). It is warm, and it receives most of the total phosphorus load to the lake because of the size of the Detroit and Maumee Rivers. Since 1994, the Western Basin has received 61 percent of the whole lake annual total phosphorus load, while the Central Basin and Eastern Basin received 28 percent and 11 percent, respectively. As a result, algal blooms dominated by the blue-green alga (cyanobacteria) Microcystis aeruginosa occur regularly, fouling shorelines during spring and summer. This species can form blooms that contain toxins (e.g., microcystin) dangerous to humans and wildlife.
  • The Central Basin is deeper with an average depth of 18.3 meters (60 feet) and a maximum depth of 25 meters (82 feet). Here the excess phosphorus contributes to hypoxic conditions (low oxygen) in the cold bottom layer of the lake (the hypolimnion) when algae die and decompose. The biological activity uses up the oxygen during the summer, leaving little to none for the aquatic community which suffocates or moves elsewhere creating Lake Erie’s “Dead Zone.”
  • The Eastern Basin is the deepest of the three basins, with an average depth of 24 meters (80 feet) and a maximum depth of 64 meters (210 feet). Here, the excess phosphorus contributes to the excessive growth of Cladophora. Cladophora isn’t toxic, but it is a nuisance and may contribute to human health problems. Beyond clogging industrial water intakes and degrading fish habitat, rotting mats of Cladophora on beaches encourage the growth of bacteria and are a factor in beach closures. The presence of Cladophora may create an environment conducive to the development of botulism which results in bird and fish deaths.

Lake Erie Basin. Credit: Environment Canada.