Yes, there are other saltwater pools in reefs with good snorkeling, but not this many spreading over so many acres on the Big Island's Puna (east) coast. The Waiopae Tidepools Marine Life Conservation District is its own place.
Smooth (pahoehoe) lava surrounds most of the pools, so you end up swimming and then walking over low lava sundecks. Coral heads grow farther out, but visibility is better closer to shore. Water depth is around four feet or shallower, depending on the tide. Swimming is normally safe, but watch out for big waves breaking over the outer reef. The tidepools are growing zones for all sorts of marine life.
Some parking is right on the rough shore, surrounded by beach homes, but the easier and more scenic choice is to park in a shaded neighborhood just beforehand and take a pretty access trail for a short distance. Either way, your three bucks will be well spent.
Travel Tip: Don't confuse these tide pools with the Kapoho Pools and 'Champagne Pool,' which are just up the road.
The marine district swim is part of a full day of adventuring in Puna. The best hot lava hikes are down here—as is the most underrated drive in Hawaii: the Kehena-Pohoiki Scenic Coast. Hawaii the Big Island Trailblazer has the details (there's a lot more to do).