Late spring through early autumn — May to October — is the best window for hiking and the lake. July and August are warm and reliably dry, with temperatures in the seventies Fahrenheit.
Autumn is the salmon season: from mid-September through November the Chinook and coho push up the creek through the hatchery in the middle of town. Issaquah Salmon Days, on the first weekend of October, is the city's biggest event and draws crowds for the fish ladder and a community parade.
Winters are wet, mild, and grey rather than snowy. The trails get muddy but stay open year-round.