Längelmävesi (Finnish pronunciation: [ˈlæŋːelmæˌʋesi]) is a lake in southwestern Finland.

The lake is located mostly in the Pirkanmaa region at an elevation of 84.2 metres (276 ft).

Längelmävesi is within the municipalities of Jämsä (formerly Längelmäki), Kangasala (formerly Sahalahti), Kuhmalahti, and Orivesi.

[1] Längelmävesi lake is part of the Kokemäenjoki drainage basin (watershed).

From the southeast, another chain of lakes (Hauhon reitti), consisting of Lummene, Kuohijärvi, Kukkia, Iso-Roine, Hauhonselkä, and Ilmoilanselkä lakes joins into the Vanajavesi.