The prairie pothole region encompasses the northern portion of North America’s grassland biome, totaling approximately 300,000 square miles. Throughout the region, retreating glaciers left about 25 million depressions of various sizes in their wake, or about 83 potholes per square mile. This density of wetlands is unmatched on the continent. Formerly a paradise for waterfowl, prairie chickens, whooping cranes, bison, wolves and other wildlife, changes to the landscape resulted in loss of more than 99% of native prairie and drainage of over 80% of the small wetlands. The region remains a critical waterfowl production and migration area, providing the highest waterfowl nesting density in Minnesota. The complex of wetlands and surrounding prairie produces more than 50% of ducks hatched in North America. The District restores grasslands and wetlands on privately owned property with landowners and preserves prairie wetlands complexes on 44,000 acres of Waterfowl Production Areas in western Minnesota.