In 2022, Alaska began replacing a fish-blocking culvert with a 100-foot bridge at Little Tonsina River with a $1.3 million budget. 1 year later, 70.4 miles of salmon habitat were reopened to fish safely

In 2022, Alaska began replacing fish-blocking culverts on the Little Tonsina River with a 100-foot bridge. The project received $1.3 million in federal Bipartisan Infrastructure Law funding. The old crossing restricted fish movement and had suffered damage during earlier flooding.

By August 2023, the new bridge was open and the river could flow more naturally beneath it. The project restored access to 70.4 miles of salmon spawning and rearing habitat, benefiting Coho and Chinook salmon. It also improved the road crossing’s resilience to floods and debris.

The project shows how replacing aging infrastructure can serve both people and wildlife. Instead of forcing fish through a narrow culvert, the bridge gives the river more room to function as it naturally should.

Alaska Bridge Project Reopens 70 Miles of Salmon Habitat

Culverts can look like simple pieces of road infrastructure, but rivers do not always behave simply. Water moving through a narrow or poorly designed crossing can become too fast for fish to swim against. Steep outlets and sudden drops can create another obstacle for salmon moving upstream. Alaska officials had identified the Little Tonsina culverts as a fish-passage barrier.

The site had other problems besides fish movement. High stream flows frequently overtopped the culverts, while debris could plug the openings. During heavy rain and seasonal breakup, that created risks for the road crossing itself. The 2006 flood showed what could happen when the river became stronger than the infrastructure built across it.

The Alaska Department of Transportation ultimately designed a different approach. Instead of forcing the river through two barrels, the project moved toward a channel-spanning bridge. That allows water, sediment, woody debris and wildlife to move with fewer restrictions.

What does the bridge mean for salmon?

The biggest ecological gain is access to habitat that already existed. The Little Tonsina River drains toward the Tonsina River, which eventually connects with Alaska's Copper River system. That watershed supports important Pacific salmon populations and provides extensive spawning and rearing habitat.

The Fish and Wildlife Service identified the crossing as its highest-priority barrier removal project in Alaska. Its importance came largely from the 70.4 stream miles above the barrier. Those miles provide places where young salmon can grow and adults can reproduce.

Removing the barrier does not guarantee that salmon numbers will rise. Fish still face many pressures across their lives, including other barriers and changing river conditions. What the project does is remove one known obstacle and give salmon access to habitat they could not reliably reach before.

Why was a bridge better than another culvert?

The answer is partly about fish, but it is also about water. A bridge can leave more of the natural channel intact instead of concentrating the river through a restricted opening. That becomes especially valuable when heavy rainfall, snowmelt or other high-flow events send much more water downstream.

The finished structure is a single-span bridge about 103 feet long. It was designed using U.S. Fish and Wildlife Service guidance for road crossings that consider fish passage and flood resilience together. The structure was also designed to handle a 100-year flood event.

That combination is what makes the project interesting beyond Alaska's salmon. It shows that wildlife infrastructure does not always have to compete with human infrastructure. In some places, rebuilding the road crossing properly can solve both problems at the same time.

Who helped make the Little Tonsina project happen?

The project brought together federal agencies, Alaska officials, conservation groups and other regional partners. The Copper River Watershed Project played a leading partnership role, while agencies including NOAA, the Bureau of Land Management and Alaska Department of Transportation contributed to the broader effort.

Funding was also assembled from several sources. The Fish and Wildlife Service lists $1,318,604 in National Fish Passage Program funding for the project. The project also received major support through the Bipartisan Infrastructure Law and contributions from other partners.

The Little Tonsina bridge was the first fish-passage project funded through the Bipartisan Infrastructure Law to break ground in the United States. Its construction therefore became part of a much larger national effort to address barriers that divide rivers and wildlife habitat.

Could this project lead to more salmon restoration?

That may become one of its most useful legacies. The Fish and Wildlife Service has identified 21 additional anadromous crossing sites within the interior Copper River watershed. Together, those locations represent another 91 miles of potential salmon habitat and more than 1,500 lake acres.

One successful crossing cannot fix an entire watershed. It can, however, demonstrate what becomes possible when transportation needs and fish passage are planned together. The Little Tonsina project already provides a working example of that approach in a remote Alaskan landscape.

There is also a practical lesson for communities far from the Copper River. Across the United States, aging culverts can become weak points when rivers flood or change course. Replacing them with better-designed crossings can protect roads while restoring connections between fragmented habitats.

The river now has more room to behave like a river

The Little Tonsina project did not create 70.4 miles of new salmon habitat. Those waters were already there, waiting upstream of a difficult crossing. What changed was the barrier that stood between the fish and that habitat.

That distinction is important because restoration often begins with removing something rather than building something new. Here, removing two restrictive culverts allowed a wider bridge and a more natural river crossing to take their place. The same project now serves people traveling across the road and salmon moving beneath it.

For Alaska, the value may extend beyond this one river. If additional barriers across the Copper River watershed can be addressed in the same way, isolated improvements could eventually become a connected restoration effort. The Little Tonsina River shows how one crossing can become a starting point for thinking much bigger about an entire watershed.