The lake lies at the altitude of 1090 m, has a surface of 7,48 hectares, a perimeter of 1242 m and the maximum depth of 18,30 m. The volume of retained water is 617 000 cubic metres. Its moraine dam is 30-40 m high and the stone sea falls some 150 metres below the lake. The glacial cirque sinks into the north-east slope of the highest mountain of the Czech part of the Šumava - Plechý. The lake wall is 260 m high. The cirque was hollowed by a slope glacier - one of eleven existing in the Šumava in the Quaternary period and with its width of 1 km the widest one. After the glacier receded, the moraine of huge boulders remained in its place and formed a natural dam here. Water of the lake drains by the Jezerní stream to the Vltava. The moraine wall was sealed in 1789-1791 and complemented with the 2,5 m high dam with flood-gates enabling regulated drain of water to the Schwarzenberg Floating Canal. This enabled releasing of some 177 thousand cubic metres of water in total from the lake.
In the mid-1990's the lake surface uncontrollably decreased due to the unprofessionally constructed outlet mechanism. The National Park Administration implemented repair works on the dam in 1999, thus partially returning natural character to the place. The Institute of Hydrobiology of the Academy of Sciences of the CR installed a measuring profile beneath the outlet, which is automatically registering outflow from the lake. A small meteorological station recording the same data as in 1930's is placed on the dam.
In 1911, Lucemburská chalet was built on the lake dam, which later became the property of the Czech Tourist Club. The building was seized and adapted by the Border Guard in 1948. The Border Guard later abandoned the chalet and it was demolished in 1989. Over the north-west lakeside, high on the top of the side cirque rocky wall, there is the Stifter's Memorial. Plešné Lake today belongs amongst the most visited places of the Šumava as the view of the water-level with the imposing lake wall in the background is very attractive. Also Johann Nempomuk von Schwarzenberg visited the place on 13th August 1868, which is commemorated by a stone plaque placed on the spot he was observing the surroundings from.