Why Are Fish Ladders Stair Stepped?

Fish ladders are devices constructed at dams that consist of a series of water-filled boxes that allow fish to travel upstream to bypass the dam. The main advantage of these stepped devices is that they enable the fish to gain access to the upper waters from the lower waters near the dam.

  1. Purpose of Fish Ladders

    • When dams are built, the resulting structure often prevents fish that migrate upstream to spawn--such as alewife, salmon and trout--from doing so. The fish have no way to get from the lower waters beneath the dam to the waters above the dam. This can be detrimental to fish populations, as they cannot reproduce as needed. Fish ladders are constructed to help fish move past the dam so they can continue upstream to spawn.

    History of Fish Ladders

    • The earliest recorded effort of people helping fish pass river obstructions such as dams occurred in France in the 17th century, according to Bronx River Alliance website. Bundles of branches were placed in the river to help the fish pass through the waters. Richard McFarlan, the owner of a water-powered mill, patented the first version of a fish ladder in 1837. Studies of the efficiency of fish ladders began in the 1970s, with researchers trapping and tagging fish at the ladders' entrances and exits to measure how many were passing through.

    Reasons for Step Construction

    • Fish ladders are constructed as steps for a very simple reason: They allow the fish to safely pass through the fish ladder without too much effort. Consider that the fish are swimming against falling water and are traveling up an incline. The job of the fish ladder, according to Bronx River Alliance website, is to break the work load into doable, flowing units of exertion with spaces in between to provide the fish rest.

    Stepped Ladders Provide Solutions

    • A prime example of the stepped fish ladder doing the job it is meant to do is the Wolf Creek fish ladder in Montana. According to the Montana Fishing Outfitters Conservation Fund website, many rainbow fish were beginning to pool at the lower end of Wolf Creek, an important spawning stream for the Missouri River. The fish were blocked by a rock barrier that had been constructed, and they would leap onto the rocks, unable to move upstream. A fish ladder was designed and built by Montana Fish &Wildlife Parks, allowing the fish to jump between the stepped pools to gain access to the upstream waters of Wolf Creek.

    Viewing Fish Ladders

    • The mechanics of stepped fish ladders can be viewed at the Sixth Street dam near Grand Rapids, Michigan, as well as at the Berrier Springs dam at Berrier Springs, Michigan. The Michigan Department of Natural Resources has constructed these ladders with viewing in mind, allowing the public to easily observe the process of various fish species, including Chinook and coho salmon, steelhead and carp, as they ascend the ladders, climbing and leaping from pool to pool.