Hanauma Bay is a small, horseshoe-shaped bay located in Koko Head, a prominent headland at the southeastern end of Oahu. Measuring approximately one-half mile form shore to its outer points and one-third mile from point to point, it contains a shallow fringing reef and a white sand beach approximately 2,000 feet long and 100 feet wide. Park facilities include restrooms, showers, picnic areas, snack bar, snorkel rental, tram service, park office, lost and found, and parking. The University of Hawaii has an educational counter where staff members answer questions, hand out brochures, and conduct hourly walking tours at no charge. A fee is charged for parking and for entry to the beach.

Hanauma means curved bay. Hanauma Bay was created when the ocean breached the seaward side of a volcanic crater and flooded the crater floor. During the thousands of years that followed the breach, the erosive force of the ocean collapsed the seaward crater wall, and a massive reef and white sand beach formed at the head of the bay, creating one of the most popular snorkeling, scuba diving, and swimming sites in the world. The reef and the deeper waters in the outer bay are home to one of Hawaiis most diverse and abundant populations of fish life.

Hanauma Bay is a marine life conservation district with strict regulations prohibiting all consumptive activities within its boundaries. Signs detailing the restrictions are conspicuously posted in the park, and park rangers can answer questions regarding the restrictions. Smoking is prohibited beyond the scenic lookouts. During periods of high surf, powerful waves surge across the low lava terraces that lead out to the points on either side of the bay. When these conditions occur, the lifeguards close the gates across the terraces. Be careful walking on the terraces even when the gates are open, and pay special attention when you are crossing sections that are already wet from the wash of previous waves. Lifeguards are on duty daily. Check with them before proceeding beyond the beach if you are walking on the terraces or snorkeling beyond the reef.