External water quality concerns are closely linked with local urban development, local sewage discharge, commercial shipping traffic, and potential oil spills. Six of the NPS units with coral reefs have indicated a high threat of oil spill pollution from the proximity of shipping lanes. Boat groundings or improper boat anchoring has caused major harm to resources in NPS units with coral reefs. Boat groundings and anchor damage are major management concerns in five such parks. Ship groundings on coral reefs in Biscayne, Dry Tortugas, and Virgin Islands national parks in the last ten years caused massive destruction, other impacts, and alterations of the reef structure.
Full recovery requires hundreds of years.
Also of concern at these and other parks is damage of the coral reefs from numerous groundings and improper anchoring by small recreational boats. Parks deal with this issue by marking designated anchorage, requiring the use of mooring buoys, and public education.