Ružinovské jazero is the city's main urban lake — a large, clean body of water in the Ružinov district, about 3 km east of the old town. The lake and surrounding parkland are the main outdoor swimming destination for Bratislava residents in summer. The water is clean, there are sand and grass beaches, and the atmosphere is relaxed and unstuffy.
The park around the lake has been steadily improved and now includes walking and cycling paths, volleyball courts, and a series of cafes and restaurants. Weekend afternoons in July and August can get crowded, but the park is large enough to absorb the numbers.
Getting there takes about 15 minutes by tram from the old town (lines 7 or 9 toward Ružinov). The lake is a good option for a warm afternoon when the old town gets stifling.