Summer (late June to August) is the obvious season — the archipelago and national park are at their best, boat hire is available, and the harbour comes alive. The lake water warms enough to swim by late July.
Spring is good for Tiveden: the birdlife is active, the ravines are full of snowmelt, and the park is quiet. Autumn brings good mushroom foraging in the forests and fine colour in the birch trees. Winter is cold and dark but the archipelago freezes solid in most years, making for excellent cross-country skiing across the ice.