Dictionary of Ichthyology  

weir = 1) nets or fences set in streams or along the coast to direct fish into a holding container for easy capture. Some weirs take advantage of the falling tide to capture fish; others catch upstream migrating adults; others strain fish out of the water on a screen through which the water drains, or into bags suspended from the screen; along a chute with a bag or box at its end; or in an arched weir, higher in the middle to direct water laterally, to the shore ends where a trap awaits the fish.
Herring weir made of brush at Eastport, Maine, National Marine Fisheries Service, Washington. Photograph by Brian W. Coad.

Canadian Museum of Nature