Walchensee fills a tectonic valley, part of the Bayerisches Synklinorium (Bavarian Syncline) and from rocks of the Triassic period (the main dolomite, Plattenkalke, and Kössener layers).

Together with the artificial inflow (see "Peculiarities"), the lake has a catchment basin of 780 square kilometres (300 sq mi).

On the eastern shore lies the Jachenau, a long alpine valley that stretches in the direction of Lenggries.

Between Herzogstand and Jochberg is little Kesselberg, which because of its relatively low prominence appears as a depression between the two higher peaks, but actually separates Walchensee from Kochelsee, 200 metres (660 ft) below.

Directly on the west bank of the lake is the tiny Luftkurort settlement of Walchensee, with only about 600 inhabitants.

Walchensee belongs to the municipality of Kochel as do the yet smaller settlements of Urfeld at the northern tip of the lake, Zwergen on the western shore, and the houses of Einsiedl am Walchensee on the orographic left bank of the Obernach at the far southwestern end of the lake.

During the summer months, heat on southern side of Herzogstand and Jochberg create strong thermals on sunny days.

In contrast to a foehn, when a katabatic wind blows from south to north, the associated dry air ensures excellent visibility.

Since the 1950s, Walchensee has become a popular destination for day trips from Munich and other upper Bavarian cities as well as for tourists.

The clear waters with an average visibility of 8–10 m owes its turquoise-green color to the relatively high proportion of calcium carbonate.

The nutrient load on the originally oligotrophic Walchensee has declined since the mid-1980s, due to improvements in sanitation in Mittenwald.

More than 50% of the fish species that live here are threatened or at least endangered in Bavaria, including the wels catfish and Rutilus meidingerii.

In addition to red-necked and black-necked grebes, mallards, and Eurasian coots, common mergansers and great northern divers are sometimes seen.

Unicellular organisms both vegetable (diatoms and green algae) and animal (water fleas, genus Cyclops ) occur in virtually all areas of the lake.

Native Phragmites and Schoenoplectus grow near the shore and waterlilies Nymphaea alba and Nuphar lutea offer shelter for grass snakes and other animals.

Creation of thermals is encouraged by winds from the East or North and by the relatively large day and night temperatures.

The clear waters with visibility of up to 40 metres (130 ft) and a whole series of car, boat, and even aircraft wrecks make the lake particularly interesting for scuba divers.

The lake is owned by the Bavarian State and is managed by the Genossenschaft oberbayerischer Berufsfischer & Teichwirte.

In 1924, Bayernwerk AG put the Lake Walchen Power Plant into operation on the south shore of Kochelsee.

In order to increase the amount of water available for the plant, a 7-km long tunnel was driven in the Karwendel to tap the Rißbach and Isar rivers, feeding Walchensee.

Two smaller hydroelectric plants were built directly on Walchensee: one at the mouth of the Niedernach in the southeast and one on the Obernach in the southwest.

Large amounts of water are only taken from lake during winter months so as not to disturb the tourist industry during the peak season.

The high-wing twin-engine plane with the markings D-ID MON crashed into the lake on 27 December 1978 after its tail broke off.