Lake Galgauskas, Koruļezers is located in Lejasciems parish of Gulbene district, 4 km north of Galgauskas, south of Gulbene - Smiltene road. Area 30.5 ha, length 1.1 km, average depth 2.3 m, maximum depth 4.2 m.
A bayy lake, narrow at the SE end, wider (450 m) at the NW end, where there is a small island and a stream flows into the Gauja. The shores are flat, overgrown with bushes. Surrounded by wavy, sandy moraine plains, forests. Eutrophic lake, ~ 15% of the surface is overgrown.