Hanauma Bay is a marine sanctuary on the southeastern part of Oahu and is home to different species of colorful tropical reef fish. It is a beautiful, horseshoe-shaped, aquamarine bay and one of the most visited and photographed beach in Hawaii. The word Hanauma means "the curved bay."

This nature park is very popular with residents and visitors alike because of its clear and calm waters. It also has a reputation of being a world-class snorkeling site.

The aquatic life in Hanauma Bay is protected by state law that fishing is not allowed within this nature park. Also, no one could not take anything out of the area and bring it home as a souvenir. The fish here became so tame and used to visitors that they will eat right from your hand. However, feeding the fish is no longer allowed. It is okay to watch the fish but not touch or bother them.

The bay was formed about 6000 years ago when the sea level rose and a side of Koko Head’s crater collapsed which allowed the sea to rush in and curve the outline of the present bay. It is approximately one-half mile from shore to its outer points and one-third mile from point to point. It has a white sand beach about 2000 feet long and 100 feet wide and nearby are found the park facilities which include showers, restrooms, snack bar, and a concessionaire where snorkling equipment can be rented. From the bus stop and parking area above, access down to the beach is through a narrow one-lane paved road where you can either ride a tram or just walk.

The Hanauma reef stretches across the entire bay and separates the shallow area of the bay from the deep ocean. The reef and the deeper waters in the outer bay are home to one of Hawaii’s most diverse and abundant population of fish life.

In the middle of the bay is a large, sandy-bottom pool within the reef known as the "Keyhole." When viewed from the cliffs above, it appears to resemble a key hole, hence its name. The reef in this part protects the bay from the open ocean and the placid lagoon close to the beach is quite popular for swimming and snorkling.

On the left side is a small tidal pool that is continuously fed with sea water passing through underwater lava tubes which causes the water level to rise and fall as the ocean waves surge into the bay. It creates swirling waves which appear to flush and fill the pool that many refer to it as the "Toilet Bowl." Also of interest are the waters on the right side of the bay which is called "Witches Brew" because it appears muddy or cloudy when the sediment within the area is stirred as the surf turns rough.

Hanauma Bay is open daily from 6:00 a.m. to 6:00 p.m. except on Tuesdays when it is closed all day. There is no admission fee for residents of the State who present a State ID or a driver's license, however there is a $1 parking fee charged for each vehicle entering the park. Non-residents are charged $3 per person to enter and use the park.