Ahalanui Beach on the Big Island is not one of the beaches you might imagine when you think of Hawaii, with its miles of sugar-fine white sand and surf lapping at your feet. This is a man-made thermal lagoon that was constructed with federal funds after lava flows from Kilauea, one of the island’s most active volcanoes, destroyed the famous Kalapana black sand beaches on this part of the coast in the 1990s.

Ahalanui Park is also known as Pualaa County Park. It is located about 30 miles south of Hilo. It is right on the ocean but separated from the ocean waves by a low wall made from lava rock. The cooling waves do wash over the wall, which is what keeps the water, fed by natural springs that are thermally heated by the volcano, at a balmy temperature of about 90 degrees. If you are deciding when to go to Ahalanui Beach on the Big Island for the warmest water temperature, try to get there just after a high tide on a day with low surf. Since there are good snorkeling and scuba diving spots in the vicinity, this is a great place to warm up and relax after day of underwater activity. In fact, some of the best snorkeling on the Hilo side of the island can be found nearby at the WaiOpae Tide Pools Marine Life Conservation District.

Although the bottom of the Ahalanui Park pool is sand mixed with mud, the water is often quite clear, and you can see that you are swimming around with colorful tropical fish. You can even do some relatively tame snorkeling here. The water is a bit brackish, and sometimes has the slight sulfur smell common at thermal hot springs. The beach here is mostly black sand, and it is shaded by palm trees and lush tropical foliage. The park for Ahalanui Beach on the Big Island is a full three acres—the pool itself is half an acre. There are grassy shaded areas for picnics, restrooms, barbecue pits, picnic tables, and ladders for easy access into the pool. There is ample parking and admission is free. The pool is generally not very crowded as it is relatively remote, so it can be a relaxing, inviting spot to end your sightseeing and hiking in nearby Volcanoes National Park. And you have wonderful ocean views as you relax in the warm waters.

Big Island Map

There is a lifeguard on duty during the day, but there is access after dark, and that is a popular time to use the pool. If it’s after dark, you should take care to swim with another person and bring a flashlight. Also be aware that there can be nude bathers after dark. Another safety consideration if you intend to use the pool at Ahalanui Park is that all thermal hot springs used by people contain bacteria, and you should not swim in the waters if you have open cuts or sores or if you have a compromised immune system. Other attractions in the vicinity, in addition to the snorkeling spots, include Lava Tree State Monument in the Nanawale Forest Reserve. Here is where a fast moving flow of lava engulfed ohia trees during the 1790 eruption of Kilauea. Today they are ghostly specters encased in hardened lava and covered with moss. There is a marked hiking trail through the seventeen-acre park.