The Riedensee nature reserve is located in the Rostock district about one km north of Kägsdorf and two km west of Kühlungsborn-West. The reserve is the remnant of a water-filled depression that was formed after the last ice age where a bog influenced by salt water was formed. The post-glacial rise in sea level, coastal recession, and changing salinity levels constantly reshaped the area around Riedensee. In the process, wind and waves formed a wall of sand and gravel and sealed off the depression from the Baltic Sea. Even today, there is no peace and quietness at Riedensee: during storm tides, the waves break through the barrier, and salty Baltic Sea water spills into the lake. At times there are openings between the sea and the Riedensee. Since there are hardly any natural beach lakes left on the Baltic Sea, the Riedensee was designated as a nature reserve in 1993. Today, the 110-hectare protected area includes the beach lake (Strandsee), adjacent dunes, salt marshes, beaches, and the Baltic Sea near the coast. As the "Riedensee FFH Area", the nature reserve is one of the European protected areas with international status. The Strandsee is one of the priority habitats that only occur in Europe and are threatened with disappearance.