The Prairie Pothole region, over 300,000 square miles, exists in the northern Great Plains and extends well into Canada. These are small depressions of varying depths that filled with water from melting glaciers about 12,000 years ago. The last glacier was a sheet of ice more than a mile thick that extended as far south as Nebraska and Iowa. That glacier deposited soil and rocks leaving thousands of depressions that filled with water. This created a rich area for wildlife, especially ground nesting shore birds. Unfortunately most of these wetlands have been drained so the land can be farmed.