Lake Guostas, located in the eastern part of the Prienai district, is one of the glacial lakes in Lithuania. It stretches approximately 2 km in a northwest-southeast direction, with a width of up to 0.63 km. The deepest part of the lake, in the southeastern section, reaches a depth of 33.7 meters, while the depth in the northwestern part is up to 18.5 meters. The lake's shores are steep and high, surrounded by dense forests: to the south, the Būdai and Lieponys forests; to the east, the Gilužis forest. The lake's shore is narrow and gravel-covered, with little aquatic vegetation. The lakebed is clay. The Guostė stream, a tributary of the Verknė, flows through Lake Guostas, connecting it with the nearby Lake Gelužis. Nearby Lake Guostas are the villages of Riešutinė, Užuguostis, and Užukalnis. Along the northwestern shore runs the 1812 Žiežmariai–Nemaitonys–Stakliškės road, and on the southern shore, you will find a recreational area and three rural tourism homesteads.