Fish ladder

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.

There are five basic types of fish ladders.^[1] 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.

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.

• Wikipedia:Fish ladder