Usma lake is a lake in western Latvia, one of the largest in the country. There are several settlements on the banks, the largest of which is Usma (Ausmas).
There are islands in the lake (in descending order of area): Viskužu, Morica, Lielalknites, Mazalknites. The islands cover an area of 4.2 km², and Viskušu is the largest lake island in Latvia.
In the western part of the lake, the Moritzala nature reserve was created in 1912.