doubled in around 30 years. The killer shrimp (Dikerogammarus villosus) has spread since 2002 from two sections of shoreline near Hagnau and Immenstaad, over the whole Lake Überlingen (2004), the whole of the Upper Lake (2006) and almost the whole Lake Constance and Rheinsee shore (2007). As its name implies, it is a voracious burglar of fish larvae and fish eggs. The most recent example is the little opossum shrimp (Limnomysis benedeni), only six to eleven millimeters long, which was found in 2006 in the Vorarlberg region of Hard, and can now be found almost all over Lake Constance. It comes from the waters around the Black Sea. It was presumably first transported by ships up the Danube before it spread into the Rhine river system and entered Lake Constance. The opossum shrimp, which occurs in many places in shoals of several million in winter, are already an influential link in the food chain in Lake Constance. They consume dead animal and plant material as well as phytoplankton, but are also eaten by fish themselves. Today, in western Lake Constance are found: the North American spinycheek crayfish (Orconectes limosus), which was introduced into European waters in the mid-19th century to increase the yield, occasionally the Chinese mitten crab (Eriocheir sinensis), and in the lake's tributaries, the signal crayfish (Pacifastacus leniusulus). As these species of large crayfish are immune to crayfish plague, but spread the pathogen, they are a great danger to native species such as noble crayfish, white-clawed crayfish or stone crayfish. The animals are often undemanding, multiply rapidly and lead predatory lives, thus also posing a threat to various small species of fish. The ISF has been systematically researching the subject since 2003. Wrecks on the lake bed After a collision with the Stadt Zürich in 1864 the wreck of the Jura has lain on the lake bed at a depth of 45 metres off the Swiss shore. In the early 20th century four ships were sunk in the Obersee after being taken out of service: in 1931 the Baden, formerly the Kaiser Wilhelm, in 1932 the Helvetia, in 1933 the Säntis and in 1934 the Stadt Radolfzell. The hull of the burnt-out Friedrichshafen was scuttled in 1944 off the mouth of the Argen in 100 to 150 metres of water. Tourism, leisure and sports The tourism and leisure industry is important for this region. Overnight stays reached 17,56m