The best time to visit Mount Gambier is between November and March, when the Blue Lake is at its most vivid blue and the weather is warm enough to enjoy the outdoor walking tracks comfortably. Summer temperatures are mild compared to the rest of South Australia — the city sits at 63 metres elevation and draws cool air off Bass Strait, so maximum temperatures rarely top 30°C even in January.
The lake colour change itself is one of the more dramatic natural events in South Australia. It happens rapidly each November — visitors who arrive a week apart can see genuinely different lakes. If you want to witness the transition, late October to early November is the window to aim for, though the exact timing varies by a few weeks from year to year.
Winters are cool and damp, with temperatures dropping to around 5°C overnight. The cave systems and the gaol remain interesting year-round regardless of weather, and the Limestone Coast wine region's cellar doors are open through winter too. The Generations in Jazz festival, held each May in Mount Gambier, is one of Australia's longest-running youth jazz competitions and draws large audiences; accommodation books out well in advance for that weekend.