Maui has reef on three sides and each side has a different season. That single sentence explains most of the disappointment visitors report about snorkelling here, because a bay that is glass in July can be a closed-out surf break in January, and the guidebook photograph was taken in the other half of the year.
The west-facing coast from Olowalu up through Kāʻanapali, Honokōwai, Nāpili and Kapalua is the island's snorkelling heartland. It sits in the lee of Mauna Kahālāwai, the West Maui Mountains, which block the trade winds for most of the morning, and the reef comes close enough to shore that you can wade in. The south shore, from Keawakapu through Wailea to Mākena, has the same lee-side advantage and the clearest water on any developed coast, with reef fingers running out from between the sandy bays. The north-facing bays, Honolua above all, are superb from roughly April to October and off the table in winter when north swell turns them into one of Hawaiʻi's serious point breaks.
The other variable is wind, and on Maui wind is a clock rather than a season. Trades typically fill in mid-morning and blow through the afternoon, which chops the surface, drops visibility and pushes anything floating along the shore. Snorkellers here plan around that clock, not around the tide. Get in the water by 8am and you are looking at a different ocean from the one at 2pm.
What you actually see is worth setting expectations for. Hawaiʻi is a young, isolated archipelago, so the reef is less elaborate than the Caribbean or the Coral Triangle, with fewer soft corals and more hard lobe and rice coral over lava. What it has instead is endemism: roughly a quarter of Hawaiʻi's reef fish exist nowhere else on the planet. Yellow tang in schools of hundreds, ornate butterflyfish, Moorish idols, saddle wrasse, parrotfish, moray eels, the occasional whitetip reef shark asleep under a ledge, and the humuhumunukunukuāpuaʻa that the state named as its fish. Green sea turtles, honu, are common and protected. In winter you will hear humpback whales singing through the water from almost any site on the leeward coast, which catches most people off guard the first time it happens.
Two rules govern everything below. Maui County requires mineral sunscreen, meaning zinc oxide or titanium dioxide, and nothing else can legally be sold or used here without a prescription. And you do not touch, chase, ride or feed anything, least of all the turtles.
