A fish ladder (or fishway, fish pass) is a structure designed to allow fish the opportunity to migrate upstream over or through a barrier to fish movement. The very best fish passage is the complete removal of the barrier but many times this is not possible then fishways can be installed to allow fish passage over or around the barrier. Fish ladders may be recommended when blocking structures are as low as 1 to 2 feet in height. Critical components to determine when a ladder is necessary are the water depth below the blockage, the height of the barrier, the water velocity over or through the barrier, are fish being blocked from moving upstream, and which species are being blocked that need to pass.

Why Do We Need Fish Ladders?
It was recognized long ago that obstructions in rivers such as dams fragment aquatic ecosystems and affect fish populations. Michigan's rivers are fragmented by over 2500 impassible registered dams and likely twice as many other barriers such as unregistered dams and poorly designed culverts. Fragmentation of rivers can and has resulted in the decline of fish production from those waters and in some cases a complete loss of fish species. Most fish species are affected by fragmentation but species such as steelhead, Chinook salmon, or suckers that are required to mitigate to spawning grounds are particular susceptible to declines from impassable river obstructions. Thus, effective fish passage can be critical to the protection and recovery of many fish stocks.

What Factors Need to be Considered When Designing a Fishway?
Many design factors are looked at by engineers when designing and placing a structure. Every barrier in a river represents a unique situation and challenge, and each fish ladder is therefore carefully designed and placed. No one fish ladder design will accommodate all species of fish at every location. Each species has different physical characteristics that need to be taken into consideration when designing passage facilities. Trout and salmon have exceptional burst speeds so they can swim through fast water. Species like walleye, northern pike and smallmouth bass lack such burst speeds and require slower water to get around or over barriers. Flows, energy dissipation, resting areas, drop between pools (fishway slope), attraction velocities, entrance locations, and space in pools are just some of the factors that need to be considered when designing a ladder.

Types of Fish Ladders or Fishways
There are five basic designs for fish ladders that are used throughout the world: pool-weir; vertical slot; Denil; steeppass; and natural bypasses or fishways. All five can be found in Michigan.

Pool-Weir Fishway
The pool and weir fishway is used at many man-made structures and are the oldest of the fishway designs. They all have a set of steps and often have a hole (orifice) in the bottom of each baffle to control plunging effect and to allow another way to fish to move upstream. This design is frequently used at larger barriers. Pool-weir designs work well for jumping species like trout and salmon and are not as effective for species that do not jump, particularly if the ladder does not have an orifice in the bottom. This fishway type is sensitive to water surface elevation changes in the impoundment or upstream river.

Pool-Weir Fishway at Berrien Springs Dam
St. Joseph River, Berrien County, MI

Vertical Slot Fishway
Vertical slot ladders are quite common and use a large narrow slot to control water flow and depths in the pools between slots. The vertical slot opens have a constant flow pattern at all operating depths and is not sensitive to impoundment or upstream water surface elevation changes. Its design is less simple than a pool and weir design, but its advantage is that it is self regulating in terms water depth for each pool between baffles with changes in flow volume. This design allows fish to pass any depth and is effective for a wide range of species as long as current speed in the baffle is not too fast. This design is frequently used at larger barriers.

Vertical Slot Fishway at Niles Dam
St. Joseph River, Berrien County, MI

Denil Fishway
Denil fish ladders use what is often described as a roughened ramp approach which is a different approach from one using pools with weirs or vertical slots to pass fish around barriers. The ladder has a large number of baffles that act like a set of rapids to a fish with a wide range of water speeds so many fish species can successfully use this type of fishway, if properly designed. This fishway can also handle a wide range of changes in the upstream water surface elevation either in the impoundment or river. You can see this design at either small or large barriers.

Denil Fishway at Trout Creek Dam
Trout Creek, Ontonagon County, MI

Steeppass Fishway
Steeppass fishways use the same principle as Denil fishways and use many baffles to simulate a rapids to a fish and present the fish with many options with respect to water speeds. This type of fishway, when properly installed, can pass a wide range of fish around barriers. These are typically pre-fabricated out of metal in 10 foot sections and are usually narrower than Denil fishways. They work best at small barriers where inexpensive passage is needed. This fishway can also handle a wide range of changes in the upstream water surface elevation either in the impoundment or river.

Steeppass fishway at Little Platte Lake Dam
North Branch Platte River, Benzie County, MI

Steeppass fishway in Alaska

Natural Bypasses or Fishways
This design looks much like a natural stream and has the ability to move all species when designed properly. A stream channel using natural materials is designed to bypass a barrier. It can replace lost stream rapids areas from impoundment, can provide replacement stream habitat, and can be used on any sized river but does require the most space to properly site it. They can also provide canoeing or boating access around a barrier such as a dam.

Natural Bypass Fishway at Williamston Dam
Red Cedar River, Ingham County, MI