Längelmävesi

 is a lake in southwestern Finland. The lake is located mostly in the Pirkanmaa region at an elevation of 84.2 m. Längelmävesi is within the municipalities of Jämsä (formerly Längelmäki), Kangasala (formerly Sahalahti), Kuhmalahti, and Orivesi.

Geography
Längelmävesi lake is part of the Kokemäenjoki drainage basin (watershed). It is one of a chain of lakes (Längelmäveden reitti) that includes Längelmävesi, Vesijärvi, Roine, Pälkänevesi, and Mallasvesi lakes. This chain of lakes drains into the Vanajavesi in Valkeakoski.

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

In Finnish, the former chain of lakes is called Längelmäveden reitti and the latter Hauhon reitti as it runs through the former municipality of Hauho.

In culture
In Finnish culture, Längelmävesi and Roine lakes are well known — as they are mentioned in the famous poem "En sommardag i Kangasala" (Kesäpäivä Kangasalla) by Zachris Topelius and have thus became part of Finnish national landscape imagery.