For 20 years, a road culvert blocked fish in California’s Sharber-Peckham Creek; crews replaced it in 2016, and 2017 monitoring found 740 juvenile coho upstream

In Northern California, a four-foot metal pipe blocked salmon from reaching upstream spawning and rearing habitat for 20 years. According to the California Fish Passage Forum, the small culvert on Galaxy Drive created a three-foot fall and a 4.9% gradient, forming a barrier for migrating coho salmon and steelhead and preventing them from moving up the low-flow tributary known as Sharber-Peckham Creek. Biologists observed adult salmon struggling to move past the barrier. However, this is not an isolated incident.

One pipe, one outsized problem

Sharber-Peckham Creek flows into the Trinity River near Salyer (Trinity County) and is the biggest contributor of coho salmon between the Hoopa Tribe Reservation and North Fork Trinity River. Coho salmon are already classified as threatened under federal law along much of the West Coast. In 20 years, the salmon were unable to get into some of the best spawning and rearing habitats in the Lower Trinity.

A solution was found in 2016. The old culvert was replaced with a new 12x14 foot buried culvert. This new structure could withstand a 100-year flood whilst also preserving the natural stream bed. The project cost approximately $297,000 and was funded by multiple organisations, including federal, state, and non-profit. These included the U.S. Forest Service, NOAA Fisheries, and the California State Coastal Conservancy.

Fish were seen almost instantly

By 2017, U.S. Forest Service monitoring had found 740 juvenile coho rearing in the newly opened section of water, 1.2 miles of the creek’s roughly one-mile total habitat corridor that had previously been blocked, per the California Fish Passage Forum account. The rapid recolonization showed how quickly salmon can return to habitat once a barrier is removed.

This isn’t a one-pipe problem

Unfortunately, this is just one example. The U.S. has a vast number of culverts, and many of these have become problematic over time. A 2024 U.S. Geological Survey synthesis study titled “Effects of Culverts on Habitat Connectivity in Streams—A Science Synthesis to Inform National Environmental Policy Act Analyses,” published in Scientific Investigations Report, found that whilst dams receive most of the attention, there are far more small culverts crossing roads. These cause just as many issues to streams by blocking fish from getting to their cold water refuges, spawning grounds and over-wintering areas.

The study also found that the most impactful barriers had a few key characteristics. These include narrow channels, high outlets, and high velocities. This was what caused the blockage on Sharber-Peckham Creek. However, correctly replacing a culvert can be very expensive. There are thousands more to replace across the country. Fixing fish passage problems nationwide therefore remains a slow, resource-intensive process, even as individual projects like this one can produce measurable results.

Proving it works without disturbing any fish

A study conducted in 2023 found that using environmental DNA to monitor if culverts are working can be successful. Researchers from the University of Washington and NOAA found that they were able to find a distinct increase in salmon and trout DNA upstream of one of the new culverts installed. The second barrier was not quite as bad and only showed minimal change. This suggests that not every culvert needs to be replaced with the same urgency and expense, the better path forward may be identifying which culverts are actually acting as barriers before committing to costly replacements.