Lake Gulbju (also referred to as Gulbītis) is a freshwater lake located in the eastern part of Ģibuļu Parish, Talsi Municipality, close to the A10 highway (Rīga–Ventspils) and the village of Spāre. The lake covers a surface area of 115.5 hectares, with an average depth of 1.5 meters and a maximum depth reaching 2.1 meters (some historical hydrographic sources note up to 4.0 meters). It features a predominantly sandy bed with low, partially steep shores surrounded by pine forests.
The lake's outflow into the Sudmaliņupe (Briežupīte) is regulated, connecting with the Kāņupe and ultimately discharging into Lake Usma. Lake Gulbju is a popular location for recreation and licensed angling, inhabited by perch, pike, tench, roach, carp, and crucian carp. On its southeastern shore lies the Joint Stock Company "Latvia's State Forests" (LVM) recreation center "Spāre", along with an 8-kilometer walking trail around the perimeter of the lake.