The Great Barrier Reef Marine Park helps to protect the world's largest coral reef, which stretches 1,240 miles (2,000km) in length. But, heavy recreational use -- camping, fishing, diving, boating has resulted in reef damage from anchors, trash, coral and shell collecting and decreased fish populations. In some areas, the reef has been dredged and blasted to provide boat access. A resort on Heron Island is believed to have caused a drop in live coral cover from 41% to just 8% because of tourists walking on the reef. Scientists are studying whether population explosions coral-eating crown-of-thorns starfish are due to increased sewage from development.