ZHAW builds spawning grounds to help Lake Zurich char

Researchers at Zurich University of Applied Sciences (ZHAW) are creating artificial gravel spawning grounds to help endangered lake char reproduce in Lake Zurich, SRF reported. The fish, also known locally as Rötel because of its reddish colour, has few suitable places to lay its eggs.

In November 2025, the team laid gravel at two locations: near the Au peninsula and off Meilen. Researchers selected the spots after checking conditions including water temperature and oxygen levels, to make sure the eggs could survive there.

Lake char need coarse, sediment-free gravel. The gaps between the stones allow eggs to settle out of reach of predators such as burbot, while also providing good oxygen conditions. Researchers say many natural spawning grounds have disappeared as sediment has accumulated, and fresh gravel rarely reaches the lake naturally.

The team is monitoring the new beds with underwater cameras and measuring conditions such as temperature and water currents. It has regularly recorded individual lake char near the gravel, but has not yet observed pairs forming or reproduction. It is therefore still unclear whether the fish are laying eggs at the new sites.

Young fish from the cantonal fish farm are also being released into the lake.