Great Lakes water quality

The Great Lakes basin is one of the Earth's largest freshwater systems, containing 18 per cent of the world's fresh surface water (EC 2001a). Less than 1 per cent of the water is renewed annually by precipitation, surface water run-off and groundwater inflow.

Over the years, the lakes have been subject to a polluting mix of effluents due to inadequate sewage treatment, fertilizer and wastewater effluent. By the early 1970s, beaches were smothered with algae and water was unfit for drinking unless extensively purified. Lake Erie suffered from excess phosphorus, algal blooms and serious declines in fish populations. Aboriginal communities were the most affected. Newspaper headlines in 1970 declared that 'Lake Erie is Dead' (EC 1999b, EC 2001c).

Other clues pointed to more insidious problems. In the early 1970s, eggshells of the double-crested cormorant, which is high on the aquatic foodchain and subject to the effects of bioaccumulation, were some 30 per cent thinner than normal (EC 1999b). Some species of bird populations crashed.

The International Joint Commission (IJC) released a report on the pollution problem in the lower Great Lakes in 1970. The IJC, an independent organization of Canadian and US representatives, has been in charge of assessing water quantity and quality along the boundary between Canada and the United States since 1909 (IJC 2000a). The report led to the 1972 signing of the Great Lakes Water Quality Agreement (GLWQA) and the beginning of concerted efforts to restore water quality. In 1978, the GLWQA was renewed to introduce the ecosystem approach and to address persistent chemical discharges (IJC 1989).

In 1987, targets or strategies for phosphorus load reductions, airborne pollutants, pollution from landbased activities and the problems of contaminated sediment and groundwater were set. Remedial Action Plans (RAPs) were developed to clean up 43 areas of concern (see map).

Municipal phosphorus loadings to Lakes Erie and Ontario have been reduced by almost 80 per cent since the early 1970s, slowing algal growth and decreasing the extent of oxygen depletion in bottom waters. Once thought 'dead', Lake Erie now has the world's largest walleye fishery (EC 1999b, EC 2001c).

Discharge of a number of persistent toxic chemicals was also reduced. Since the late 1980s, government regulations achieved an 82 per cent reduction in chlorinated toxic substances discharged from pulp-and-paper mills. Since 1972, there has been an overall reduction of 71 per cent in the use, generation and release of seven priority toxic chemicals and a significant reduction in chemical spills (EC 1999b, EC 2000, EC 2001c).

DDE and PCB residues, once exceptionally high in cormorant eggs in the Great Lakes basin, decreased by as much as 91 per cent and 78 per cent respectively between the early 1970s and 1998 (EC 2001b). Cormorant populations are breeding successfully again and other bird populations are increasing (EC 1998, EC 1999b).

Rapid urban and industrial development, however, continued to cause environmental damage to the watershed during the 1990s. Sediment contamination in harbours and river mouths threatened to contaminate fish and posed problems related to dredging and sediment disposal (IJC 1997). Evidence revealed that pollutants carried in the air settle on the lakes, contributing significantly to water pollution (US EPA 1997). Up to 96 per cent of PCBs in the Great Lakes come from the atmosphere (Bandemehr and Hoff 1998). The Great Lakes Binational Toxics Strategy was launched in 1997 to eliminate these chemical contaminants (BNS 1999, EC 2000b).

Although exposure to persistent toxic contaminants has decreased, some studies show that children of mothers who ate large quantities of Great Lakes fish had development problems (Health Canada 1997). Recent IJC reports warn of slow progress with some problems, such as the clean-up of sediments containing persistent toxic chemicals and exotic invasive species (IJC 2000b).

The Great Lakes will face other environmental challenges in the future. Global warming could lower lake levels by a metre or more by the middle of this century, causing severe economic, environmental and social impacts. Water shortages throughout North America may also increase pressure to divert or remove water in bulk from the lakes, threatening the sustainable use of surface and groundwater resources IJC 2000c, IPCC 2001).