Known from lakes Zürich and Walenstadt. At present there is a homogenous population in Lake Walenstadt which spawns October - November. Fifty years ago, there were two populations, one spawning July-September and the other December-February. The winter-spawning population is said to have appeared in 1899. It has been hypothesized that displacement of spawning grounds, changes in temperature, and possibly invasion by a species from Lake Zürich resulted in a hybrid population (involving 2 or 3 species), which is now stabilizing after severe environmental problems which impacted the lake at the beginning of the 19th century (Ref. 59043).