A weir consists of interlinked panels that stretch across the whole river. The type of weir shown
in this photograph consists of floating panels that are anchored to the river bottom on the
upstream side. This allows water to flow through, but stops the upstream passage of fish. The
center of the weir has a chute with a gated holding pen. As salmon swim into the pen, biologists
count the fish and identify the species, then release them to continue swimming upstream to
spawn. Some of these fish are also measured and the sex is determined.