in a hydroengineering complex, a structure enabling fish to pass upstream, mainly during the spawning migration. Fishways are divided into two basic groups: structures enabling fish to independently pass an obstacle (fish passes) and structures that move fish (locks and fish elevators).

Fish passes are channels through which water flows downstream at a speed making it possible for the fish to swim against the current. There are three basic types of fish passes: trough, pond, and ladder. Some trough passes have slight gradients, smooth walls, and a smooth bottom. The bottom and walls of others are fitted with projections. Another type of trough pass has incomplete partitions (in terms of depth and width).

Pond passes consist of a series of basins, where the fish can rest during their journey. The basins are connected by short channels or troughs. The passes usually are built in the banks, bypassing the dam.

Fish ladders are in the form of stepped troughs divided into a series of basins by cross-partitions having flotation openings. This type of fish pass has proved most effective for many different species of fish.

A dam on the Tuloma River (USSR) has a fish ladder for Atlantic salmon (height, 20 m; length, 513 m), and the McNary dam on the Columbia River (United States) has a ladder for salmon (height, 25 m; length, 610 m).

Fish locks in terms of operation are similar to ship locks. Ordinarily they have two adjacent chambers, each of which has gates separating the chambers from the upper and lower waters. The locks can operate under significant head. However, they require large amounts of water, and their fish-passing capacity is relatively low.

Fish elevators, which lift the fish in a moving flooded chamber or in a special net, operate according to the same principle as mechanical ship-lifting apparatus. Fish elevators, like fish locks, are usually located in separate piers of the dams. Also used as fishways are hydraulic fish elevators, floating fish-lifting devices, and, sometimes, ship locks and spillways of hydroelectric power plants.

It is advisable to locate fishways around the spillways. To guide the fish away from dangerous areas and toward the entrance of a fishway, guiding and protective nets and screens are set out. The subsequent descent downstream of the fish and their young is made possible through the use of all types of fish passes, hydraulic fish elevators, low- and medium-head spillway dams, ship locks, and the water channels of hydroelectric power plants equipped with adjustable-blade and mixed-flow turbines (with a large-diameter rotor, a slow turning speed, and significant clearance between the rotor and the stator). The designs for fishways in modern high-head hydroelectric projects are still insufficiently advanced.