Zhoushan has the best beaches in Zhejiang, concentrated mainly on Zhujiajian Island and the outer islands of the southern archipelago. The sand is finer and the water cleaner than at most beaches on China's northeast coast, because the islands sit south of the main Yangtze outflow that muddies the sea closer to Shanghai.
Zhujiajian's Dongsha Beach is the most accessible and best-equipped, with a long arc of pale sand, rental facilities, and restaurants along the front. Daqingshan Island, a smaller island south of Zhujiajian, has quieter beaches reachable by short boat crossing from Shenjiamen. The Shengsi Islands at the outer archipelago have rocky coasts more than beaches, but the isolation compensates for the limited swimming.
Water temperatures are comfortable from late June through September; the sea is cold but swimmable in May and October. July and August bring the highest waves and the most domestic tourists; spring and autumn are uncrowded and the sea is still warm enough to swim in.