An estimated 14,000 tons of sunscreen is believed to be deposited in oceans annually with the greatest damage found in popular reef areas in Hawaii and the Caribbean. In 2015, the nonprofit Haereticus Environmental Laboratory surveyed Trunk Bay beach on St. John, wherevisitors ranged from 2,000 to 5,000 swimmers daily, and estimated over 6,000 pounds of sunscreen was deposited on the reef annually. The same year, it found an average of 412 pounds of sunscreen was deposited daily on the reef at Hanauma Bay, a popular snorkeling destination in Oahu that draws an average of 2,600 swimmers each day.
Sunscreen alternatives …[with] mineral sunblocks with zinc oxide and titanium dioxide ..must be “non-nano” in size to be considered reef-safe. If they are below 100 nanometers, the creams can be ingested by corals.