Lake Mikołajskie is a glacial lake covering about five square kilometres, stretching 5.8 kilometres from north to south with a maximum depth of 26 metres. It is one of the most popular sailing lakes in Poland, and the waterfront at Mikołajki fills with masts and rigging from late May through September. The lake connects to Lake Tałty to the north and Lake Śniardwy — Poland's largest — to the south through a system of straits and canals, making it the hub of a much larger cruising ground.
Boat hire is available from several marinas on the Mikołajki waterfront. Sailing dinghies, kayaks, pedalos, and motorboats can all be rented by the hour or the day. Excursion steamers make scheduled runs to other lakeside villages and to the Łuknajno nature reserve. The lake freezes most years between January and March, when ice sailors and kite-skaters take over the surface.