Alteration to dam improves fishery

in Lake Huron

A 60-year-old dam on the Potagannissing River, located on northern Lake Huron’s Drummond Island, was modified to permit fish passage and bolster the region’s northern pike fishery.


A dam built in 1947 on the Potagannissing River was designed to create a marsh for waterfowl. But the dam unintentionally blocked fish passage, which contributed to a decline in the northern pike population on Drummond Island and in the St. Marys River, which links Lake Superior and Lake Huron. The Michigan Department of Natural Resources installed a fish ladder in 1999, but northern pike were unable to navigate the structure. So the DNR removed three feet from the top of the dam and built a series of four rock-ramp structures, which allowed all species of fish to swim over the dam and reach prime spawning habitat areas upstream.

Resource Challenges Addressed

  • No fish passage
  • Loss of spawning habitat
  • Altered stream flow


fish steps in a river to replace a removed dam

Rock steps were placed in the river to allow fish passage over the dam remnants. Credit: Tim Cwilinski Michigan Department of Natural Resources.

Results and Accomplishments

Providing fish passage at the dam was expected to increase the number of northern pike in the Potagannissing River and Potagannissing Bay, which is part of the St. Marys river. Modifying the dam gave fish access to 800 acres of high quality habitat on Drummond Island. Biologists said it would take several years for the northern pike fishery to realize the benefits of the dam modifications.