Lake St. Moritz

At about 1,768 metres above sea level, Lake St. Moritz forms the downstream end of the four Upper Engadine lakes. Lakes Sils, Silvaplana and Champfèr sit higher, making St. Moritz the lowest in this chain, not an altitude record-holder. The cantonal report gives a maximum depth of 43 metres for this natural basin. FOEN lists a 171-square-kilometre catchment extending well beyond the town itself.

The Inn connects Lake St. Moritz to the lakes upstream and then continues down the valley. Part of that descent generates electricity: the Islas power station uses roughly 51 metres of head between the lake and the Celerina plain. A regulating weir and water intake are therefore part of today's water system. Hydropower use does not, however, make this naturally formed lake an artificially created high-mountain storage basin.

The published lake-protection agreement provides for regulation that keeps summer fluctuations as small as possible. An annual cycle remains visible: monthly averages for 1991–2025 are 1,767.84 metres above sea level from February to April and 1,768.01 in June. That roughly 17-centimetre difference compares historical monthly averages; it is neither an authorised operating range nor a forecast for any particular year.

For lake level, use St. Moritzersee–St. Moritz station 2066, which measures water-surface elevation. An Inn station describes a river section even if it shares the same place name. Meaningful comparisons require the correct station and unit. Neither an elevation near 1,768 metres nor a small daily rise directly reveals the depth at a shoreline location or the power station's current output.

Cantonal surveys for 2014–2021 again classified Lake St. Moritz as nutrient-poor, yet deep-water oxygen deficits persisted at the end of summer stratification. The report also documents winter measurements beneath ice. Surface temperature alone therefore does not describe the lake's condition. Historical ice observations do not establish whether today's ice can bear weight; current local access authorisations are what matter.