Kalaülekäik

Kalaülekäik, which translates to "fish passage" or "fish ladder" in English, is a general term for structures designed to allow fish to bypass natural or man-made obstructions in rivers and streams. These obstructions can include waterfalls, dams, weirs, culverts, or natural rapids that impede fish migration. The primary purpose of a kalaülekäik is to restore or maintain fish populations by ensuring they can reach their spawning grounds upstream and access feeding areas downstream.

There are various types of fish passages, each designed to suit specific environmental conditions and fish species. Common examples include fish ladders, which are inclined channels with a series of steps or pools that reduce the water velocity, allowing fish to swim upstream. Fish lifts or elevators use mechanical systems to transport fish over barriers. Denil ladders, a specific type of fish ladder, utilize angled baffles to create turbulence that allows fish to swim up even with relatively high water flow. Culvert modifications, such as adding baffles or roughening the interior surface, can also improve passage in culverts.

The effectiveness of a kalaülekäik depends on its design, maintenance, and the behavior of the target fish species. Factors like water flow, depth, and the presence of sufficient resting areas are crucial for successful passage. Environmental agencies and conservation organizations often implement and monitor these structures as part of broader efforts to manage aquatic ecosystems and protect migratory fish species. Understanding fish behavior and hydraulics is essential for designing functional and efficient fish passages.