Prairie Pothole Region, large geographic area of central North America consisting of grass-covered wetlands. Stretching northwest from N Iowa through SW Minnesota, E South Dakota, E and N North Dakota, SW Manitoba, and S Saskatchewan to SE and E central Alberta (and including bordering areas of N Montana), the region is covered with thousands of shallow, sometimes seasonal ponds known as potholes or sloughs, which were created when continental glaciers retreated more than 10,000 years ago. The area is the summer home and breeding grounds of some 45 million mallard, pintail, gadwall, and teal ducks as well as many other shore-, song-, and gamebirds, and is popular with hunters and birdwatchers. Located in an important agricultural region, the ponds were routinely drained by farmers to plant wheat and other crops prior to 1985, and the bird and wildlife population had fallen precipitously. The 1985 U.S. federal farm bill, however, provided for conservation subsidies and, in a "swampbusters" provision, withdrew agricultural subsidies from farmers who drained wetlands. As a result, grass replaced wheat in many parts of the region, providing habitat for birds and other animals and leading to an increase in their populations. The program also aided the efforts of family farmers to keep their land by providing funds that counteracted economic losses resulting from low grain prices.