Thousand Islands in August

May through October gives you the full experience, but timing matters. Late May and early June offer decent weather without the summer crowds crushing popular spots like Boldt Castle. July and August bring peak everything – warmest water, longest days, and shoulder-to-shoulder tourists at every castle tour. September hits the sweet spot with fewer crowds, comfortable temperatures, and the start of fall colors reflecting off the water. October can be spectacular for leaf peeping, but boat schedules start winding down after Canadian Thanksgiving. Winter essentially shuts down tourist operations, though ice fishing draws hardy locals. Spring comes late here – April still feels like winter, and black flies make May challenging for hiking. The water doesn't really warm up for swimming until late June, despite what the tourism brochures claim.