The islands almost divide the lake into three parts, one of which is occupied by the Moricsala Reserve, which is rich in flora and fauna. Moricsala is inhabited, similarly to Viskūžu Island. Despite its depth, it has many shallow places. The shores of the lake are mainly sandy. There are forests, recreation centres and campsites in the area.
Thetypesof fish living in the lake include pike, carp, bream and perch. Usma Lake is fed by ten rivers – Tīrukšupe, Godele, Melncelma, Meķupe, Sērža, Ostupe, Baņģava, Struncene, Riekte and Kāņupe. There is a nature reserve not far from the lake. The area of the reserve is 3469.2 ha.