When the last glaciers receded from the Northern Great Plains 10,000 years ago, they left behind shallow depressions called potholes. Some prairie potholes hold water temporarily, while others hold water year-round. These wetlands nurture a variety of insect and plant life, which in turn attracts great numbers of waterfowl, including ducks and geese, and other wildlife. At least half of North America's waterfowl breed in the Prairie Pothole Region. These prairie wetlands not only help produce the next generation of ducks and geese, they also help conserve water for people by reducing flooding through capturing and holding snowmelt, recharging the groundwater, and helping ensure that water is available for drinking and irrigation during drier periods.