Lake Łuknajno (Łuknajno Reserve) is a UNESCO Biosphere Reserve and one of the most important nature sites in Poland, lying just east of Mikołajki. The shallow lake is ringed by reed beds and bordered by alder and willow woodland, creating habitat for one of the largest mute swan populations in Europe. In moulting season (June–July), thousands of swans gather here; through the year the lake attracts bitterns, marsh harriers, white-tailed eagles, and dozens of other waterbird species.
Access to the lake shore is strictly controlled — visitors use designated viewing points and a limited network of paths. A watchtower near the main entrance gives a view over the reed beds toward the water. The reserve is a short cycle or drive from Mikołajki and is well worth the hour. Do not attempt to access the lake outside designated areas — the warden service is active.