FISHBIO staff have been using weir technology since 1999 to research and monitor various migratory fish species throughout California. Like a fence across a river, weirs create a temporary barrier in a channel and direct migrating fish through a single opening where they can be enumerated (such as with a Vaki Riverwatcher fish counter) or trapped. FISHBIO has fabricated both portable resistance board and rigid weir designs for variety of applications.

A resistance board weir consists of an array of rectangular panels made of evenly spaced PVC pickets aligned parallel to the direction of flow. The upstream end of each panel is hinged to a rail, which is anchored to the substrate. The downstream end of the panel is lifted above the surface by a resistance board that planes upward in flowing water. When all components are installed, the resulting barrier inhibits fish from migrating upstream except through the passing chute, yet allows water to pass. A passing chute on one of the panels guides fish into a livebox where they can be visually counted, electronically counted or captured, before being allowed to pass upstream. The portable nature of modular panels makes the weir relatively easy to install and remove.

Rigid weirs consist of panels made of pipes or pickets that requires some infrastructure to hold them in place against the current. This is usually accomplished by using A-frame tripod structures or cabling to hold the rigid weir panels upright. Our FABLAB has experimented with other rigid weir designs, including ​​adjustable legs that hinge onto the panels. One benefit of a rigid weir design is that they more easily allow fish to pass in both upstream and downstream directions. Contact us to learn more about our weir construction capabilities.


Peterson, M.L., A.N. Fuller, and D. Demko. 2017. Environmental factors associated with the upstream migratory activity of fall-run Chinook salmon in a regulated river. North American Journal of Fisheries Management 37: 78-93. DOI: 10.1080/02755947.2016.1240120

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