Drive almost to the east end of Kalanianaole Avenue in Hilo to find Richardsonʻs Beach Park.
Despite regular human visitation to this black sand beach park for decades, fish diversity here is very high. And there seems to be something that enormous green sea turtles find attractive, as well, often grazing on algae so intently that snorkelers nearshore can receive the whack of an impatient flipper.
Swim straight out from the lifeguard tower to get your bearings and check for currents, then investigate the lovely and delicate reef in the shallows to the right (but never touch them) or follow surgeonfish and butterflyfish on their daily business over the central and more rocky reef.
Winter conditions tend to be rougher than summer.