Swimming upstream: Why culverts for fish passage are an important element of wildlife and habitat connectivity

May 11, 2023

By Rachael Hamby

In the Western U.S., migratory habitat and corridors for big game species have gotten a lot of attention in recent years. In 2018, then-Interior Secretary Ryan Zinke signed a secretarial order which directed Interior department agencies to work with Western states to identify, conserve and restore migratory habitats for big game species. Several states soon followed suit with their own policies and funding to identify, protect, and connect migratory habitat and corridors. In 2019, the New Mexico state legislature passed the Wildlife Corridors Act, requiring the state to develop a Wildlife Corridors Action Plan. The state followed up in 2023 with an appropriation of $5 million to support implementation of the plan. Also in 2019, Colorado Governor Jared Polis signed an executive order that required the state’s Department of Natural Resources to report on migratory corridors and habitats and to identify policy opportunities to improve corridor conservation. The next year, Wyoming Governor Mark Gordon designated three migration corridors and laid out a process for future corridor designations. Then in Nevada, former Governor Steve Sisolak created the Nevada Habitat Conservation Framework, which includes the development of a Nevada Wildlife Connectivity Plan.

A wildlife overpass in Nevada. Nevada Department of Wildlife

These and other efforts to protect and connect wildlife habitat and migration routes are overwhelmingly popular. According to the Colorado College State of the Rockies 2023 Conservation in the West poll, 85 percent of Westerners support investing in the construction of crossing structures to help migrating wildlife, and more than 90 percent of voters in all eight states polled say that preserving habitat and migration routes for wildlife is an important reason to pursue conservation efforts.

As important as land migration corridors are, they are not the only piece of the puzzle. Just as roads fragment habitat and block big game species from moving along migratory corridors, they can also block passage for fish and other aquatic and riparian species. When a road crosses a stream, in many cases the stream is funneled through a culvert. Culverts can take a variety of forms, but many of these prevent fish and other species from moving farther up the stream. This prevents fish from reaching upstream spawning areas, and reduces the quality and diversity of habitats and ecosystems upstream of these barriers.

An example of a perched culvert, which is a virtually impassible barrier for most species. Even if a fish can get into the pipe, the water in the pipe is too shallow and moving too fast. Brendanboshea, Wikimedia Commons, CC BY-SA 4.0

Solving this problem can be as simple as removing problematic culverts and replacing them with bridges — which allow water to flow freely — or other structures designed with fish and other aquatic and riparian species in mind. Following culvert replacement projects, fish recolonize upstream habitat almost immediately. Other species benefit as well: with these barriers removed, other aquatic species such as salamanders and frogs have more habitat accessible to them, and riparian and terrestrial species can continue traveling along the stream without having to cross the road. In some instances, culverts can be replaced with bridges large enough to allow even large animals to pass underneath.

A culvert with a ramp for terrestrial species passage. U.S. Forest Service

People and communities benefit from culvert replacement projects too. The replacement projects themselves create design, engineering, and construction jobs. A completed culvert replacement project creates better river access and results in better habitat upstream, expanding and improving fishing and other outdoor recreation opportunities. These replacement projects can also improve safety and hazard mitigation; for example, a poorly designed culvert that previously resulted in flooding on the road can be replaced with a structure that is better able to accommodate high water. Many aging culverts that need to be replaced anyway for safety reasons present opportunities to replace the culvert with a structure designed with fish passage and habitat connectivity in mind.

An example of a channel-spanning culvert which allows species and floodwater to move more freely. U.S. Fish & Wildlife Service

Despite the many clear benefits of culvert replacement projects and the need to do more, funding remains a challenge. Fortunately, several federal fish passage and culvert replacement programs received money from the Infrastructure Investment and Jobs Act (IIJA) and from the Inflation Reduction Act (IRA). In April, the Interior Department announced an investment of $35 million from the IIJA for the National Fish Passage Program, administered by the U.S. Fish & Wildlife Service. Of the 39 projects in 22 states that will receive funding, several are in Western states, including:

  • Arizona: $325,000 for the Crooked Creek Route 55 Culvert Fish Passage Project, which will replace a culvert that is currently impeding fish passage
  • Idaho: $500,800 for the Coeur d’Alene Tribe Lake Creek project which will replace five culverts, and $145,000 for the Zena Creek fish passage project which will remove a dam and restore habitat
  • Montana: $900,000 for several culvert replacement and dam removal projects on 66 river and stream miles in the western part of the state
  • New Mexico: $648,735 to repair the Hogback Sluiceway Gate to improve passage and habitat access for four native fish species
  • Wyoming: $250,000 for a retrofit of the Killdeer Diversion Dam to improve both recreation safety and fish passage
An Apache trout, one of the species that will benefit from the Crooked Creek Route 55 Culvert Fish Passage Project in Arizona, U.S. Fish & Wildlife Service

Other culvert replacement programs also received funding from the IIJA and will be announcing awards in the coming months. One such program, the National Culvert Removal, Replacement and Restoration Grant Program, administered by the Department of Transportation, is funded at $200 million per year for the next five years, for a total of $1 billion through 2026. This program is intended to benefit anadromous fish species — fishes that are born in freshwater and return to freshwater to spawn, but otherwise spend much of the rest of their lives in the ocean. These include species of trout and salmon, as well as Pacific lamprey, that are found in Idaho as well as in states on the West coast.

Many communities across the West, and many species and ecosystems, stand to benefit from these investments in jobs, road safety, hazard mitigation, outdoor recreation, and habitat and ecosystem health. It is important that the Biden administration, future administrations, and Congress all continue to prioritize culvert removal and other habitat connectivity and restoration projects to benefit wildlife and communities now and into the future.

Featured image: Middle Fork of the Salmon River, Idaho. U.S. Geological Survey