Prairie Potholes Help Keep Your Water Clean

Prairie potholes are depressional wetlands (primarily freshwater marshes) found most often in the Upper Midwest, especially North Dakota, South Dakota, Wisconsin, and Minnesota.

Sometimes called the “duck factory” of the Midwest, the prairie pothole region supports more than 50 percent of our nation’s migratory waterfowl. Most prairie potholes themselves are less than an acre in size, little more than depressions in the landscape that fill up with snowmelt and rainfall. Some of these depressional wetlands are present all year long, while others form only after rainfall. Threatened by increased agricultural protection and development, the Environmental Protection Agency (EPA) estimates that today only 40 or 50 percent of the original number of prairie potholes that covered the region remain.

Why Are Prairie Potholes Important

Prairie potholes aren’t just important for ducks. Prairie potholes recharge groundwater supplies, slowly allowing water to infiltrate into the earth over time. They also help to slow and store floodwaters, reducing the impacts of downstream flooding. In fact, the U.S. Fish and Wildlife Service found that each acre of these small wetlands reduces flood damage to roads by $6.11 every year and provides $29.23 worth of flood protection to agricultural lands.

Are Prairie Potholes Protected Under The Clean Water Act?

Right now, probably not. Two Supreme Court cases and the resulting administrative guidance put protections for these types of wetlands that might be outside of a floodplain or that lack a clear surface connection to downstream waters, sometimes called “geographically isolated” waters, into question.

However, the science is clear that prairie potholes are connected to downstream waters. For example, studies demonstrate that prairie potholes act as nutrient sinks [PDF], capturing and filtering out excess nitrogen and phosphorous from agricultural practices. When prairie potholes are filled in or degraded, these pollutants aren’t captured and downstream water quality suffers. Multiple studies show that the loss of prairie potholes results in increased flooding in the region, such as along the Red River in North Dakota, Minnesota, and Iowa.

The proposed rule recognizes this connection and clarifies that these types of waters could be protected if there is a significant connection to downstream waters. In other words, if a prairie pothole in question collectively with other similar waters would have a more than speculative effect on the biological, physical, or chemical integrity of downstream protected waters. The proposed rule doesn’t categorically protect these types of waters, but the EPA and the Army Corps are looking for the public to comment on whether that should change in the draft.