Fish ladder
A fish ladder is a structure that helps fish move past a barrier such as a dam by providing a sequence of pools, channels, or other passages.
Pool-and-weir fishway: A fishway divided by low weirs into resting pools that fish ascend in stages. Its stepped pools are the classic ladder design, with each weir limiting the jump between levels.
Fish migration: The regular movement of fish between habitats for feeding, growth, or reproduction. Many ladders are intended to preserve migrations interrupted by dams.
Fishway effectiveness: The degree to which a fishway enables target fish to find, enter, pass through, and survive it. A visible ladder does not guarantee that fish successfully complete passage.
Nature-like fishway: A bypass channel designed to resemble a natural stream and provide passage around a barrier. It offers a less ladder-like route, with a channel rather than discrete steps.
Vertical-slot fishway: A fishway with continuous vertical openings in cross-walls connecting successive pools. The slots let fish pass at different water depths as they move upstream.
Salmon: Common name for several species of migratory fish in the family Salmonidae. Salmon are prominent ladder users, especially during upstream spawning migrations.
Fish population connectivity: The exchange of organisms and genes among populations through movement between habitats. Successful passage can reconnect populations separated by a barrier.
Fish bypass: A route that guides fish around a dam or water-intake structure, often through a separate channel or pipe. Some bypasses move fish downstream, while ladders typically support upstream movement.
Denil fishway: A steep fishway whose baffles create a turbulent, slowed flow along a channel. Its baffles make a compact, fast-flowing alternative to a pool-and-weir ladder.
Eel ladder: A climbing passage designed for juvenile eels, often using a wetted, textured ramp. Eels climb differently from jumping fish, so their passages use distinct surfaces and flows.