Although some bleached reefs do return to normal, it's a lengthy process. Construction projects to build sea walls or piers, for example, may help the tourist trade in tropical destinations, but the consequences often endanger coral reefs. Human run-off in the form of sewage and fertilizers are dumped into coastal waters, as are chemicals and petroleum products. Over-fishing compounds other reef stresses, by removing creatures that ordinarily feed on algae and clean the reefs. Trash, created by humans and carelessly tossed out by humans, has negative impact.
Ocean currents deposit the refuse hundreds, even thousands of miles from their point of origin.
One recent clean-up effort on an atoll called French Frigate Shoals, netted 8.25 tons of debris including abandoned fishing nets, plastic bottles, golf balls and just plain garbage. This costly effort took numerous divers and support personnel, plus a full month to complete. Such debris seriously interferes with the health of the reefs and harms all the sea creatures. Often the most attractive and the most economically valuable reefs are those found in developing countries. These countries, however, are struggling with major challenges such as wide-spread poverty, building roads and handling sewage disposal or even government instability.