Several of Phuket's most popular day tours include snorkelling, but the quality and amount of time in the water varies more than the marketing suggests.
Phi Phi Islands
Snorkelling stops (typically around Bamboo or Mosquito Island) are usually a secondary feature alongside Maya Bay sightseeing — decent visibility, but shared with a high volume of other tour boats on the same schedule. See our Phi Phi guide.
Racha Islands
Generally clearer water and calmer conditions than Phi Phi, with snorkelling as more of the day's main focus rather than a stop alongside sightseeing. See our Racha Islands guide.
Similan Islands
Some of the clearest water of any of these options, but a longer transfer time eats into the actual time spent snorkelling on a single-day trip — better suited to a liveaboard for serious snorkelling and diving time. See our Similan guide.
Which to choose
If snorkelling quality is the main priority over sightseeing variety, Racha or a Similan liveaboard generally beat Phi Phi's more sightseeing-driven itinerary.