Beavers: blessing or dam nuisance?

A beaver swims toward the camera.

When steelhead trout swim up from Lake Superior toward their spawning streams, they sometimes find beaver dams blocking their way.

To protect the fishery, the Minnesota Department of Natural Resources (DNR) has been removing dams. But many local landowners and the DNR want to know the other impacts of dam removal. On the one hand, their ponds hold water, releasing it slowly through dry periods and raising groundwater levels. On the other, the ponds heat up water and are subject to evaporation.

“Many people like the dams because it provides habitat for a lot of other species,” say Karen Gran, UMD science professor and project lead. “Generally, the beavers are removed to help the local fishery, but it’s not clear what removing the dams does to the overall hydrology of the basin.”

The DNR is conducting a two-year study to find out. It focuses on four pairs of watersheds along the Knife River, all with active beaver populations. After collecting baseline data this year, the researchers will remove dams from one member of each pair next year. When all the data is in, scientists from UMD’s Natural Resources Research Institute will determine how dams affect steelhead spawning. The research team will then compare this impact and all the other effects that beavers exert on the environment.
University of Minnesota, Twin Cities