MANY of the world's big lakes are threatened by pollution or huge drainage schemes. But there is at least one (fairly) bright spot. The Great Lakes and the St Lawrence river system between Canada and the United States, which together account for a fifth of the world's non-polar fresh water, are much healthier than they were. Can they stay that way?
Though Lake Michigan is wholly within the United States, all five lakes are governed by the Boundary Waters Treaty of 1909, implemented by an independent binational joint commission. In 1978, both countries agreed to try to clean up the water in the lakes, several of which were heavily polluted. They have done so—though in fact the improvement owes as much to economic change as to government action. Steel and other heavy industry have given way to cleaner industries and services, both in Ontario and in American lakeside states. The result: tests on fish and birds show residues of heavy metals have declined (though dangerous levels of mercury are still found), while in the past ten years the rivers near Toronto have been successfully stocked with salmon.
There are still worries. One problem is farming. This uses much lake water (29% of the total that is withdrawn) for irrigation, while also polluting the lakes and river systems. The huge quantities of manure spread on farms in Ontario and Quebec also causes pollution, by running off the land into streams, rivers and then lakes. Neither local, provincial nor national governments have programmes to tackle this. Then there is a plan to route a natural-gas pipeline in a 150km (93-mile) trench across Lake Erie. Critics say this might disturb the toxic sediment lying on the lake bottom, while ice scouring might rupture the pipe.
Some scientists also worry that water levels will fall permanently. Climate change is likely to cut rainfall in the Great Lakes basin, while ever more water will be drawn from the lakes by a rising urban population. General consumption in the basin will increase by 25% in the next 25 years, according to a forecast by a consultant to the commission.
Other threats include some 140 exotic species of flora, fish and shellfish that have found their way into the lakes, some via ships' ballast. The zebra mussel from Eastern Europe is the most notorious and probably most damaging to the environment. It consumes a lot of oxygen (though it also helps to clean the water). Lastly, there is the hazardous prospect of decommissioning Ontario's two dozen ageing nuclear reactors, which line the shores of Lake Ontario and Lake Huron.
Fortunately, the long history of successful co-operation between the two countries and among local governments suggests these threats can be managed. The commission has long run the St Lawrence hydro-power project at Cornwall, Ontario, and regulated the river flow without dispute or political interference. In June, the governors of eight American states and the premiers of Ontario and Quebec signed an accord setting out principles for controlling bulk-water exports. They are due to work out binding rules on these within three years. Canada's Parliament is close to approving a government bill to protect boundary waters against bulk removals.
Both governments have approved the commission's plan to set up international watershed boards across the continent. These are to take a “holistic” approach to ecosystems. Maybe the Zebra mussel and the farm run-offs have met their match.