Foz do Iguaçu in July

April through September brings the best weather - less humidity, fewer mosquitoes, and water levels that showcase the falls without overwhelming them. July and August see the biggest crowds and highest prices. Book accommodations three months ahead for these months. December through March is wet season. The falls rage at maximum power but expect daily downpours and oppressive heat. March and April offer the sweet spot: decent weather, manageable crowds, and water levels high enough for dramatic photos. Avoid Brazilian school holidays in July and December unless you enjoy queuing with thousands of excited teenagers. The falls flow year-round, but September through November provides the most comfortable temperatures for hiking the trails.