NORTH KINGSTOWN, R.I. — Last month The Nature Conservancy (TNC) and the Rhode Island Department of Environmental Management (DEM) built a small wood and fiberglass structure at a fork in the Gilbert Stuart Brook, closing off a costly detour for migrating river herring.

The structure, known as a picket weir, consists of five removeable grates, resting on wooden abutments and set in the water at a 30-degree angle. Durable and easy to maintain, the structure will be stored offsite each year from June to February and then reinstalled in March, just prior to the start of the herring run.

The goal of the project is to prevent river herring from swimming into a historic mill race canal that dates to the mid-1700s. Whenever water flows over the Gilbert Stuart dam in the spring — because of heavy rain or the operation of the waterwheel — it creates a false attraction to the mill race, which leads to a dead end at the base of the Gilbert Stuart dam. As the water level recedes, the fish become stranded and perish, if not rescued by DEM staff and volunteers.

The picket weir replaces DEM’s longstanding practice of using temporary plastic fencing to deter herring from the mill race. While inexpensive, the fencing trapped debris flowing downstream and was prone to failing during high flows.

The new approach was developed by Bryan Sojkowski, a regional fish passage engineer with the U.S. Fish & Wildlife Service (USFWS), which assisted DEM through a partnership with TNC. Sojkowski noted the situation at Gilbert Stuart Museum is not unique, and if the design is successful, it could be applied on other streams in Rhode Island.

“As a fish passage engineer, I’m typically designing fishways to move fish upstream or downstream, over a barrier,” Sojkowski said. “In this case, it was the reverse. We needed to block fish from moving upstream.”

Up to 250,000 adult river herring return annually from the Atlantic Ocean and swim up the Narrow River into Gilbert Stuart Brook. The picket weir is designed to keep herring in the main channel, where they can pass through a fish ladder behind the museum to reach Carr Pond to spawn.

The work at Gilbert Stuart Museum is the latest in a series of fish passage improvement projects in South County. The TNC-DEM-USFWS project team previously corrected deficiencies at fish ladders on the Saugatucket and Annaquatucket rivers that were preventing river herring from migrating upstream.

River herring are important to the ecosystem, providing forage for ospreys, bluefish, striped bass, and many other animals.

The picket weir construction contract was awarded to SumCo Eco-Contracting of Peabody, Mass., through a competitive bidding process. The project was funded by grants from the Horace & Ella Kimball Foundation and the Narragansett Preservation and Improvement Foundation. The Gilbert Stuart Birthplace & Museum was a key partner and provided logistical support as the landowner. Total construction cost was $54,000.