By Dr. Jennifer Biederman, Habitat Director

Unobstructed pathways are crucial for stream-dwelling trout at key times throughout the year and life cycle.  Trout must be able to move freely in a stream system to reach spawning and overwintering areas, find coldwater refuge in low, warm summer flows, and access feeding grounds. However, barriers like dams, road crossings, and culverts—many built during rapid infrastructure expansion in the last century—disrupt these vital routes, particularly in northeast Minnesota, where native brook trout populations are at risk.

Poorly designed culverts, which are often too narrow or improperly sloped, hinder fish movement by creating fast currents or waterfall-like conditions that fish cannot overcome. These barriers sever the connection between streams and their floodplains, disrupting the natural flow and ecological balance within waterways.

Culverts also impact stream biology by restricting fish migration, leading to long-term genetic changes in populations and increased sedimentation, which can bury critical spawning habitats. The geomorphology of streams is altered as well, with disrupted sediment flow and increased erosion along streambanks, further destabilizing habitats. Water quality deteriorates due to increased turbidity and higher temperatures caused by “backwatering” behind undersized culverts. Additionally, the hydrology of streams is affected, with altered flow regimes and fluctuations in water depth that negatively impact aquatic ecosystems.

To address these issues, the Minnesota Trout Unlimited (MNTU) has been working with various partners to remove fish barriers in northeast Minnesota. We use the MNDNR culvert assessment protocol to prioritize replacements based on fish passage requirements. In 2023, MNTU replaced three problematic culverts in the Manitou River watershed

Extreme flooding in June across northeast Minnesota highlighted the improved resilience of streams with our recently installed culverts (the culverts did their job in passing rising waters beneath roadways). The recent flooding also highlighted the old, undersized culverts that still block fish passage and cause roadway and stream damage during high flow events across the northeast.

This August, MNTU is replacing three of these culverts, focusing on those that will best restore connectivity for brook trout. Two of these culverts are located on tributaries of the Baptism River near Finland, MN, are expected to be complete by the end of the month. The third culvert, set for construction between August 15 – September 15, 2024, is on Okerstrom Road in Hermantown, and connects two previous MNTU habitat improvement projects construction in 2021 and 2022.

MNTU is using grant funding from the Outdoor Heritage Fund to cover most of the costs of these 2024 projects. We also thank our partners including the City of Hermantown, Crystal Bay Township, and the Minnesota Department of Natural Resources Fisheries and Forestry divisions.