If you look at any of the many tourist brochures found at Maui's Kahului Airport, you will find an abundance of ocean-based activities. This is because of Maui's calm, clear waters, which are home to a large variety of sea life, 33% of which is found only in the waters of Hawaii.
Every year from December to April, Maui County becomes home to humpback whales that migrate to Maui's warm waters to mate and give birth. Humpback whales are particularly playful, breaching as well as slapping their tail and pectoral fins. Of all the major Hawaiian Islands, Maui is the best place for whale watching due to the huge number of whales that frequent the area versus other islands. There are a number of whale-watching boat tours available on Maui that leave from either Lahaina or Maalaea harbor. One of the most popular whale-watching companies is the non-profit Pacific Whale Foundation.
Maui offers some of the best snorkeling in the state of Hawaii, with clear blue waters and abundant fish life, much of which is endemic to Hawaii. Many companies offer snorkel boat tours to visit "turtle towns." These "towns" are areas where turtles congregate to get their shells cleaned by cleaner wrasse, fish that eat parasites and dead tissue off the skin of larger creatures. It is not uncommon to see a half dozen turtles in these areas. Another popular spot that cruise boats like to visit is the partially submerged offshore crater island, Molokini. Molokini is a marine reserve with great visibility, typically around 100 feet. It is home to about 400 different varieties of fish, including moorish idol, butterfly fish and triggerfish.
For a unique view of Hawaiian waters, consider taking a submarine ride. Atlantis Submarines operates a 48-passenger submarine that offers tours four times a day. Visitors board a shuttle boat at Lahaina, which takes them to an air-conditioned submarine that has large viewing windows. The submarine takes passengers to depths of more than 100 feet to see reefs such as the Carthaginian, a replica of a 19th-century supply vessel that now sits 95 feet below the water's surface. Through the submarine's viewing ports, passengers can see stingrays, bluefin trevally, sea turtles and divers who often frequent the Carthaginian wreck. If you take the submarine during whale season, you may quite likely spot the majestic humpback whale. Visitors planning to take the Atlantis Submarine ride on Maui may want to consider wearing something red and watching it change to purple because of light refraction in deep water.