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Fixing Connections Between Great Lakes and
Tributaries Doesn't End With Dams

Research shows of more than 260,000 road crossings in the
Great Lakes drainage basin, 64 percent may block fish movement

By Adam Hinterthuer
University of Wisconsin and

Ashley Spratt
External Affairs

Over the last several years, federal and state agencies and environmental nonprofit organizations have targeted dam removal as a way to quickly improve the health of Great Lakes tributaries. Dams keep migratory fish, such as lake sturgeon, northern pike, and salmon, from swimming upriver to spawn, block movement of vital nutrients, and change the way water flows. For many, taking down a dam and returning a river to a more natural flow seems like a no-brainer.

In the study, published in the current issue of the journal Frontiers in Ecology and the Environment, researchers mapped every obstacle — from large hydroelectric dams to tiny road culverts — in the entire Great Lakes drainage basin. What the maps show is that, while there are more than 7,000 dams on the rivers, creeks and streams flowing into the Great Lakes, there are 38 times that number of road crossings — or 268,818, to be precise.

“Improving the connection between the Great Lakes and its tributaries is a high priority for a broad range of conservation partners across the Great Lakes region,” said Brad Potter, science coordinator for the Upper Midwest and Great Lakes Conservation Cooperative (LCC).  “Different agencies and organizations have different roles to play, whether it’s in-stream fish habitat restoration, dam removal or modifying road crossing to be more passable,” says Potter. The LCC community, which is providing funding for the University of Wisconsin-led study on aquatic connectivity, supports cross-jurisdictional, stakeholder-driven research that helps natural resources managers improve conservation efforts across broad landscapes.

Stephanie Januchowski-Hartley, lead author of the study with the University of Wisconsin-Madison Center for Limnology, says many road crossings are bridges with minimal impact on stream flow but field studies in the Great Lakes region suggest that 64 percent of the more than 260,000 road crossings could at least partially block fish movement.

"If you're a state agency or a nonprofit group and you want to invest in river restoration and remove a dam, but you didn't consider that, upstream, there are thirty road crossings and half of them are impassable, then you have a problem," says Januchowski-Hartley. "You did do some good [by removing a dam], but to be most effective, you should think about all barriers."

“Many species of fish and wildlife require large areas to support their daily and annual activities,” Potter said. “Maintaining large connected natural areas, and restoring severed connections is one of the primary priorities for our LCC community. This research is helping us identify the significant challenges related to fragmentation in our Great Lakes rivers and streams, and providing us the information necessary to identify the most cost-effective solutions to restoration.”

Many fish want to head as far upstream as possible to spawn in small tributaries during the spring. Taking a dam out of the main-stem river gives those fish more habitat to spend their adult lives in, but may not allow them to access preferred spawning habitat that's crisscrossed by roads.

Water often shoots through the narrow corrugated metal tunnels of a road culvert so fast that fish can't swim through. In steeper terrain, "perched culverts" essentially act like mini-dams, where water spills over a ledge into the stream below. Unless those fish are high-jumping salmon, any little ledge may be an obstacle.

Januchowski-Hartley hopes having these maps available for state agencies and nonprofit groups will offer a "big picture" perspective on improving river access for migratory fish species.

Besides, she says, it's less expensive to replace a road culvert than remove a dam. "In this region of the world, it seems like just about every road gets re-done in the spring," she says, noting that there is ample opportunity to re-engineer a crossing that better fits a river or stream.

In addition to funding this research, the Upper Midwest and Great Lakes LCC serves as a venue to coordinate vested stakeholder efforts to improve connections between the Great Lakes and their tributaries, while consider all the potential impacts of in-stream barrier removal or retention. Many organizations and partnerships including the Council of Lake Committees, Council of Great Lakes Fishery Agencies, American Fisheries Society and Association of Fish and Wildlife Agencies are involved in providing guidance for site specific actions to restore severed fish movement pathways. The LCC is working toward development of a coordinated, Great Lakes wide approach to ensure the cumulative effects of all such actions are considered.

To read the full published article, visit

For additional LCC funded research on aquatic and terrestrial connectivity, visit

The Upper Midwest and Great Lakes LCC is among 22 similar partnerships that collectively form a national network of land, water, wildlife and cultural resource managers, scientists, and interested public and private organizations—within the U.S. and across our international borders—that share a common need for scientific information in conservation. For more information about LCCs, visit



Last updated: June 28, 2013