Fig. 15: The ground of Lake Zug is all covered with mussels which are continuously filtering water. This species here is the most common today and came originally from the Black Sea. Its a zebra mussel (Dreissena polymorpha). — Nikon D200, Nikkor AF-S Micro 2.0/105mm, Lake Zug, Strick, 2 July 2009 Nikon D200; Δt=1/250 s; f=105 mm; f/11.0; ISO 100; 2 July 2009 19:53:01