Each fish ladder was 40 feet wide and circled from a lower water level to a higher level. Every 16 feet there were 6-foot-high barriers to regulate the pools. Within each partition were submerged openings, 2-feet square, through which the fish could swim.

The fish-locks operated like navigational locks, with water being entered from the bottom.

"... In operation, the entrance gate first is opened and a moderate quantity of water admitted through the bottom of the chamber flows out through the entrance gate to attract fish into the chamber. The entrance gate then is closed and the chamber is filled by water admitted through the bottom. The exit gate then is opened, permitting the fish to escape to the river above the dam. A submerged grill that slopes downward toward the exit gate may be slowly raised beneath the fish to urge them toward the exit and assure their departure. The exit gate is then closed, the lift chamber drained, and the entrance gate opened for the commencement of a second cycle. The fish-locks are provided in pairs, in order that one chamber always may be open for the entry of fish. ..." [U.S. Corps of Engineers, 1939]

A "collecting system" was installed at Bonneville Dam to encourage the fish towards the ladders and locks. Auxiliary water could be released by a conduit system which increased the flow at the entrance to that of a fair-sized river.

From the U.S. Corps of Engineers "Fishways at Bonneville Dam" (1939):

"... As a means of observing the success of the fishways, fish-counting stations have been installed in each ladder. Each counting station consists of a picketed barrier in which there are three gate controlled openings, two feet wide for the passage of fish. A submerged, white platform over which the fish must pass as they leave the counting gate aids the identification of species. The counting gates remain closed except when an observer is present to count the fish. Experience has shown that there is very little movement of fish at night. Counting, there for, generally is limited to the hours of daylight, the gates being kept closed at night. During the peak of the run two or three counting station in each ladder are operated at one time. Each species of fish is counted separately and counts are recorded hourly. During the first season actual count showed 271,656 Chinook, 74,989 Blueback, 15,298 Silver, 2,107 Chum Salmon, 106,884 Steelhead Trout, 2,213 other game fish, 5,321 Shad, 376,272 scrap fish (Sucker, Squawfish, Chubs, Carp, etc.), 3,102 White Fish, and 223,248 Lamprey passing over the counting stations on the way upstream. ..."