South of Kona and west of Keokea on the Big Island, the snorkeling at Hanauma Bay State Underwater Park is popular for its visibility and gentle surf. Locally known as the City of Refuge, Honaunau Bay snorkelers commonly spot tang, parrot fish, moray eels, sea turtles and surgeon fish. The water entry is usually from the flat rocks that are at water level making for easy entry. You can even sit on the rocks while putting your fins on. The left south side of Honaunau Bay tends to be shallower and where the turtles hang out. The right north side of Honaunau Bay tends to descend quicker and to be where the spinner dolphins hang out.
Access to Honaunau Bay is provided through Puuhonua O Honaunau National Historic Park. There is not a dedicated parking area for Honaunau Bay, so you need to arrive early to grab one of the few spots at the end road (well before 9am). The bay is located about 45 minutes from the Kona airport.
To reach the snorkeling on the Big Island by air, you will need to fly into either Kona International Airport (KOA) on the south side of the Big Island and Hilo International Airport (ITO) on the northeast side of the Big Island. From either airport, the best bet is to rent a car since the dive sites are pretty far off the main roads.
The best Big Islands snorkeling dive sites are spread around the island. The conditions at each dive site vary throughout the year depending upon winds and currents. Since many of the Big Island snorkeling destinations are open water and unprotected, make sure to check the current surf reports before heading to any of these dive sites. Luckily, there are excellent up-to-date surf reports that can provide guidance on these adverse conditions. With the usually rolling surf, it is strongly discouraged to use open-tube snorkels which are common at snorkel rental locations -- only use snorkels with a dry-top splash-guard and a sump purge-valve in the mouth piece.
Overall, Honaunau Bay is the 4th most popular snorkel dive spot of all 7 snorkeling dives in Big Island.