The ruling Wednesday affirms a state Court of Appeals judgment that reversed a Renville County Board decision which said the study wasn’t necessary. The Minnesota Center for Environmental Advocacy challenged the county’s decision.

It’s unclear whether the high court’s ruling will affect other conflicts around the state involving drainage projects that preserve farmlands but increase the volume of water and pollutants flowing downstream, the Star Tribune reported.

The Supreme Court said upper Limbo Creek is a public water, and therefore an environmental assessment must be conducted before a proposed drainage project can be allowed there.

The dispute involves proposed improvements to a century-old ditch that empties into the upper reaches of Limbo Creek. Backers say the project would lead to better drainage of farmland in the area.

The Renville County Board declined in 2020 to order a review known as an environmental assessment worksheet because the creek’s upper reaches didn’t appear on the official inventory list kept by the state Department of Natural Resources.

Limbo Creek has a watershed that includes more than 14 square miles (36 square kilometers) in Renville County. It flows directly into the Minnesota River, which has long been a major contributor of silt and farm chemicals to the Mississippi River. So, according to the environmental group, an increase in stream flows as a result of the ditch project could potentially cause increased erosion and contribute to pollution as far downstream as the Gulf of Mexico.