A number of open water swimming races highlight the year, as do various lifeguard contests and much else. However, Hawaiians still treasure the ability to dive deep, spear dinner fish and capture lobsters and other marine edibles. Big game fishing is, of course, a major source of income on the Big Island where world record Blue Marlin and other species are taken from relatively flat water. It's available on other islands as well.
Locals are avid bank, reef, beach, bay and cliff anglers too.
There's even decent freshwater fishing for bass, peacock bass, trout and other species. On land, Hawaii offers some of the best camping in the US, and it's completely overlooked by the vast majority of visitors. Contact Tourism for each island, the State Park system or the National Park System for reservations. Many parks require reservations six month to a year ahead. Biathlons build up to the Iron Man on Hawaii and each weekend finds a swimming, biking or running race somewhere in the islands.