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Prairie Pothole Region
Glacier-made wetlands of the northern plains that raise much of America's ducks
Each spring, millions of shallow ponds fill across the northern Great Plains, and roughly half of North America's ducks are hatched beside them. These are prairie potholes, small wetlands scattered over about 300,000 square miles (777,000 km²) of the Dakotas, Minnesota, Iowa, Montana and the Canadian prairies. The last ice sheet of the Wisconsin glaciation made them. As it retreated about 10,000 years ago, buried blocks of ice melted out of the glacial till and left closed depressions that collect snowmelt and rain. Many hold water only for weeks, others for years, depending on the run of wet and dry seasons.
The region holds only about a tenth of the continent's waterfowl breeding habitat yet produces about half of its main game ducks in an average year, including mallards, pintails, canvasbacks and blue-winged teal. Farming has claimed much of it. North Dakota lost nearly half of its wetland acreage to drainage, and in parts of Minnesota and Iowa about 90 percent is gone. Federal Duck Stamp revenue buys waterfowl production areas and easements here, and conservation groups pay farmers to leave potholes intact. Because the ponds store floodwater and recharge groundwater, their fate also shapes flooding on rivers such as the Red and the Missouri.