Hanauma Bay Nature Preserve, Oahu, Hawaii
Hanauma Bay Nature Preserve wasn't always so clean. The state has been enforcing strict rules for beachgoers in the former volcanic crater site since 1990, and it is the first Marine Life Conservation District in Hawaii. Visitor numbers are restricted and an educational video about preserving the fragile ecosystem is mandatory before entry. Now the living reef environment is one of the top spots in the state for snorkeling.