A fish tunnel was built in the center of Stockholm. The structure is intended to enable animals to migrate between the Baltic Sea and Mälaren, one of Sweden's largest lakes. The waterway runs through a system of locks and is illuminated during the day to mimic natural conditions.
The fish tunnel is part of a project to renovate the lock connecting the Baltic Sea bay of Saltsjon with Lake Mälaren, called Slussen by locals. The system was built in the 18th century to facilitate navigation and prevent flooding, but it prevented many fish species from migrating between water bodies. This had a negative impact on biodiversity in Lake Mälaren, Sweden's third largest lake.
Rest and comfort
As explained by Slussen project spokeswoman Eva Rosman, the tunnel was built especially for species such as perch, bream, roach and pike. These fish cannot jump like salmon or sea trout, which prevented them from migrating freely from the bay to the lake.
The trail was designed by to mimic the natural environment. Its bottom is covered with stones of various sizes. Some of them come from the 16th-century defensive wall, which was discovered during excavations in 2022. The water flow is calm and controlled so that the fish can stop and rest. During the day, the tunnel is illuminated, imitating natural conditions.
The trail runs under the waterfront and is invisible from the outside, and special fences prevent seals from entering the lock. In one part of the tunnel, a camera was installed that records passing fish – and more. Among other things, she got through the fence. an otter that was tempted by the abundance of tasty fish swimming in it.
– It must have been a real smorgasbord for her, Rosman added.
Main photo source: Reuters