The Hot Spring:
At Ahalanui Warm Spring ground water heated by the Kilauea volcano seeps out of the basalt lava flows next to the ocean. The spring itself and the area around the spring is completely developed. The spring has been turned into a large concrete swimming pool with concrete sides, stairs, and a concrete wall protecting the pool from the ocean but also allowing the salt water to enter and mix with the fresh hot water. On the inland side of the pool and along parts of the bottom of the pool the basalt lava flow is exposed where the warm water is flowing out of cracks. The pools varies in temperature greatly from the inland side where it is just under 100 degrees F and near the ocean where the salt water and fresh water can mix bringing the temperature as low as 80 degrees F depending on the tide. The depth of the pool also changes with the tide varying from 8 feet deep to only 2 feet deep.
Ahalanui is part of the Isaac Hale Beach Park and is managed by the Department of Parks and Recreation. A large parking lot is built with concrete walkways, bathrooms, showers, picnic areas with barbecues, and there is even a lifeguard for the pool. Because it is part of a park it operates with park hours and is open only from 7am to 7pm. Other restrictions include no alcohol, dogs, or unattended children. This pool is also well known by the locals of the Big Island and it does not have a good reputation. It is very popular with large families that have a lot of kids, so many people said the water was dirty with piss from all the kids. When I visited there were very few people and the water felt relatively clean. I think the flow and tidal changes are large enough that the pool gets completely flushed out relatively quickly so the dirtiness of the water depends on how many people are currently at the park.