Rotopōhueroa / Lake Constance is an alpine lake in Nelson Lakes National Park, Tasman Region, South Island, New Zealand. Sitting at approximately 1,340 metres above sea level, it is considered the largest alpine lake in New Zealand, measuring around 2 kilometres long and 700 metres at its widest point. The lake occupies a large post-glacial basin and drains via an underground river into the nearby Rotomairewhenua / Blue Lake.

Paddlers planning to visit should be aware of a critical restriction: the Department of Conservation explicitly prohibits putting any equipment into Rotopōhueroa / Lake Constance. Swimming, washing, taking water, and placing any equipment in the lake are all prohibited. This restriction applies equally to the adjacent Rotomairewhenua / Blue Lake. The lakes hold high cultural significance to Māori, particularly Ngāti Apa ki te Rā Tō iwi, and are considered tapu (sacred). The restrictions exist to uphold the lakes' mauri (life force) and purity.

An additional environmental concern reinforces these restrictions: the invasive alga lindavia, which causes a sticky mucus known as lake snow, is present in nearby Lakes Rotoiti, Rotoroa, and Tennyson. Introducing even a single droplet of contaminated water via wet equipment could establish lindavia in these currently unaffected alpine lakes. DOC biosecurity cleaning stations are located at Coldwater Hut, Lakehead Hut, and Sabine Hut for disinfecting gear that has contacted lake or river water elsewhere in the park.

Reaching the lake requires a minimum of two days of backcountry tramping. The most common approach involves taking a water taxi from the Lake Rotoroa jetty to Sabine Hut, then hiking approximately 22 kilometres up the Sabine Valley via West Sabine Hut to Blue Lake Hut, with Lake Constance located roughly one hour beyond Blue Lake Hut. The lake is not accessible by road or as a day walk from any trailhead.