In 2017, California replaced a fish-blocking road crossing on Upper Green Valley Creek; surveys later found 136 young steelhead upstream of the former barrier

A small road crossing in Sonoma County once stood between young steelhead and nearly a mile of upstream habitat. The aging culvert beneath the crossing blocked fish passage to another creek. In 2017, engineers replaced this barrier with a new stream crossing designed to pass fish through. A study of Upper Green Valley Creek found that 136 young steelhead were detected above the site of the previously existing blockage, suggesting that the restored crossing helped reconnect this section of waterway. The project helped reopen upstream habitats and restore access for endangered steelhead.

The barrier hiding beneath a road

The upper Green Valley Creek is located in the Russian River watershed, which is found in Sonoma County, California, and is home to the steelhead trout species. These fish require connected streams to intermingle because they need various habitats at different stages of their lives. Young steelhead, known as juveniles, spend time growing in freshwater streams before some eventually migrate toward the ocean. They must have access to water with acceptable water parameters, shelter, and food to survive. Fish may lose use of critical areas of habitat when a road, bridge, or culvert blocks them. One such barrier was the old road crossing on Upper Green Valley Creek. The existing structure was a barrier to fish movement, particularly during low water. Even a slight fall or rapid current can prove to be a barrier for small fish.


Replacing a barrier with a natural stream crossing

The replacement of the old road crossing with a natural stream crossing provided a more continuous route for fish, allowing them to move through the creek without encountering the previous barrier. The replacement also improved the movement of water, sediment, and other materials through the creek. The natural movement of water, sediment, and other materials is important because fish habitat depends not only on water but also on the physical features of the stream, including gravel areas where fish can reproduce and sheltered places where juveniles can hide.

136 young steelhead made the new passage work

After the crossing was completed in 2017, scientists returned to check whether steelhead were using the newly available habitat. During follow-up surveys conducted in [add survey year], scientists detected 136 young steelhead above the location of the former barrier. The discovery revealed that fish had invaded areas where it was difficult or even impossible before. The identification of young fish suggested that the restored crossing allowed steelhead to access and use habitat that had previously been difficult to reach.

The wider impact of reconnecting streams

There are thousands of road crossings that interface with streams throughout the United States. Many were constructed many years ago without taking into account their impact on fish passage. For migratory species such as steelhead, a single impassable crossing can separate populations from important areas of habitat. The ability to remove and replace these barriers can reopen spawning and rearing areas that have been isolated for many years. The rewards may be greater than just fish. A well-designed stream crossing may enhance water flow, mitigate erosion issues, and permit movement of other aquatic life within the watershed.

How scientists measure long-term success

Restoring a stream crossing is the initial step. After that comes long-term monitoring, which helps researchers determine whether young steelhead that reach these habitats survive, grow, and contribute to future generations. Scientists continue to monitor studies like the one for Upper Green Valley Creek to find out if the streams that have been reopened are being utilized by fish during more than one season. These findings later guide decisions about thousands of other road crossings that affect fish movement across California.