Mnemba Atoll is the ring of shallow coral that surrounds tiny Mnemba Island, three kilometres off the north-east tip of Unguja. It is the best snorkelling and diving area on the East African coast, with consistently good visibility, dense coral cover, dolphins that habitually patrol the outer edge, and the chance of green turtles on almost every dive. Bottlenose dolphin encounters are common — boats often pause for swims with the pod, though the ethics of chasing them around are debated.
Day trips run from every lodge in Matemwe (the closest beach to the atoll, about twenty minutes by boat), as well as from further afield. Mornings are calmer; afternoons can get choppy. Snorkellers should bring their own mask if possible — rental gear is workable but rarely well-fitting. Diving operators in Matemwe and Nungwi run several daily boats; the wall on the eastern side of the atoll is the highlight.