If you look on the right side of this image of Lake Constance, you can see that the water level is about 1m lower than during summer. In spring, when the snow on the mountains melts, it is 1m above normal, and can be up to 2m higher than normal. This variance in water levels, which can amount to 2 to 5 meters every year, was the reason why the people populating the area during the bronze age built stilt houses into the lake. In the early 20th century, archeologists reconstructued such a prehistoric dwelling, which still can be visited today.