Lake Śniardwy is Poland's largest lake with an area of 113.8 km² and 23 km in length. Together with Mamry it forms the famous Great Masurian Lakes system.
Average depth 5.8 m, maximum 23 m. Stocked with vendace, burbot, eel, bream. Waters are shallow and quickly become rough — sailors call it "the Baltic of Masuria".
8 islands: largest is Czarci Ostrów (8 ha) with primeval oaks. Sandy beaches near Łuknajno (swan reserve) and Pisz. Mute swans winter here — up to 2000 birds.
Access: Mikołajki (main port), Pisz, Niedzice. Sailboat rentals from 200 PLN/day. Marked swimming areas.