The Frillensee is a small lake in the Wettersteingebirge mountains near the Eibsee. The landslide separated the Frillensee from the Eibsee. However, both lakes are still connected underground and the water level has always the same height. The name is derived from minnow (Phoxinus phoxinus) - a small freshwater fish (germ. die Pfrille).