Fish ladders (also called fishways and fish passes) are used to help fish get upstream to spawn. When dams or other obstructions are created in a stream or river, it is sometimes necessary to help the fish so that they can continue to do their part in the river ecosystem.
Types of fish ladders[edit | edit source]
There are five basic types of fish ladders. All of these examples can be found around the United States, but some are used on large waterways more often than others:
- Pool-Weir: This type of fishway design is used most often at man-made passageways and is the oldest type of fish ladder.
- Vertical Slot: The vertical slot design makes use of large narrow slots to control water flow. It is more complicated than the pool-weir type; however, it allows the water to flow at a constant rate.
- Denil: The denil fishway uses devices that regulate the flow of water. This then acts like a set of rapids with various water speeds. Therefore, this design can be used by a variety of fish species.
- Steeppass: The steeppass fishway design is similar to that of the denil; however, steeppass fishways are typically narrower than denil fishways.
- Natural Bypasses: Natural bypasses make use of materials found in nature and are intended to allow fish to bypass barriers.
Why do we need fish ladders ?[edit | edit source]
It has been found that entire fish species are either close to extinction or totally extinct because they are unable to reproduce. Some species of fish must migrate upstream to find a suitable place to spawn, and many man-made obstacles make that virtually impossible. Fish ladders allow fish to circumvent this problem and encourage natural reproduction.