Lake Łuknajno lies four kilometres east of Mikołajki and is one of the most important bird reserves in Poland. The shallow eutrophic lake supports one of Europe's largest breeding colonies of mute swans — typically several hundred pairs — along with bitterns, black-throated loons, and dozens of other species. The reserve was designated a UNESCO biosphere reserve in 1976 and is a Ramsar wetland site.
Access is on foot along a marked trail from Mikołajki or by bicycle along the lake-shore path. The reserve has an observation tower overlooking the shallow bay where the swans congregate. The best time to visit is May and June, when the birds are nesting; autumn migration brings additional species through. The lake itself is closed to boats to protect the wildlife.