The best time to visit Naivasha is June to September, when the long dry season brings cool, clear days, minimal rain, and excellent wildlife and birding conditions. Lake levels stabilise, hippo pods congregate in predictable spots, and the Rift Valley skies are brilliant for photography.
January and February are also excellent — the short dry spell delivers warm, sunny days and fewer visitors than the June–September peak.
March–May (the long rains) sees heavy afternoon downpours that can make unpaved tracks muddy, but the landscape turns vivid green and migratory birds are present in large numbers. Accommodation rates are lowest and the lake is quieter. October–November brings the short rains — still manageable, and birding remains good as resident species are joined by Palearctic migrants.
Naivasha is a year-round destination thanks to its proximity to Nairobi — even rainy-season weekends attract visitors. If you are aiming specifically for Hell's Gate cycling, avoid peak rains (April–May) when the gorge paths can be slippery.