Plitvice Lakes National Park in April

May through September offers the warmest weather and fullest waterfalls, but also the biggest crowds. July and August see 15,000+ daily visitors - arrive by 7 AM or forget about peaceful photos. Late spring (May-June) hits the sweet spot: waterfalls are thundering from snowmelt, temperatures hover around 20°C, and the crowds are manageable. September brings gorgeous autumn colors but less dramatic water flow. Winter visits are magical if you can handle icy walkways - frozen waterfalls create an otherworldly landscape, plus you'll practically have the place to yourself. Just know that some upper trails close due to snow, and daylight hours are limited. The park's microclimates mean weather can change fast, so check conditions before heading out.