Hawaii's Big Island has some of the calmest, clearest waters in the islands, the best of which can be found at Kealakekua Bay. The best snorkeling is close to the Cook monument which is difficult to access unless you kayak across the bay. Once across the bay, simply land your kayak by the monument and dive into the waters there where you are likely to see a large variety of fish, including reef trigger fish and butterfly fish. Keep an eye out for sea turtles and dolphins which frequent this area. Visibility is excellent, and according to the Hawaii Division of Aquatic Resources can range from 5 to 120 feet, making it a great place to go scuba diving as well.
Kealakekua Bay State Historical Park
Kealakekua, HI 96750
Paddling is a popular water activity throughout Hawaii. If you happen to be staying on Oahu, definitely consider renting a kayak and paddling around Kailua Bay in windward Oahu. Kailua Bay is one of the best places on Oahu to Kayak because of its calm conditions. Kailua Beach is an idyllic beach with white sand, turquoise water and pretty offshore islands. It is routinely listed as one of the best beaches of America, and was even named best beach by "Conde Nast Traveler" in 1998. Of the three offshore islands, you can paddle and land on two of those islands, Flat Island and one of the Mokulua islands, both of which are an excellent place to picnic and relax. A number of companies, including Kailua Sailboards and Kayaks, offer kayak tours around Kailua Bay.
Kailua Sailboards and Kayaks
130 Kailua Road
Kailua, HI 96734
If you are interested in a water activity with a little bit of a rush, consider going into a shark cage. Hawaii Shark Encounters on Oahu operates a shark cage tour where visitors are taken by boat three miles offshore and don snorkel gear before entering a floating cage. The cage has poly glass installed so you can get right up to the cage bars without any concern about safety. Be aware that you Are unlikely to see any Great Whites although Hawaii Shark Encounters made headlines in 2005 when a Great White did appear. However, most of the time the types of shark that you are likely to encounter are Galapagos sharks, Sandbar sharks Grey Reef sharks and, very rarely, Tiger sharks.
Hawaii Shark Encounters
66-800 Haleiwa Road
Haleiwa, HI 96712