CANBERRA — Australia said on Monday it will ban fishers from about one-third of the Great Barrier Reef to protect the world's largest living structure from the impact of humans.

The coral reef, one of Australia's main tourist attractions with its magnificent array of tropical fish, is under threat from record high temperatures, overfishing, and pollution.

Environment Minister David Kemp said the plan would increase so-called green zones, where commercial and recreational fishing is banned, from 5 percent of the 2,000-km (1,200-mile) reef to more than 30 percent, prompting instant protests from fishers.

"The Great Barrier Reef is suffering very considerable pressures at the moment from increasing usage by tourists, by fishers, by the local communities," Kemp told reporters. "It is very important that we give the reef proper protection for the future. The reef is Australia's greatest natural icon."

The Great Barrier Reef, situated off Queensland state in Australia's northeast, injects an estimated A$1.5 billion (US $975 million) into the economy each year through tourism and fishing.

Kemp said the plan, expected to be approved later this year, would boost the area subject to high protection to 114,000 square km (44,020 square miles) from 16,000 square km (6,178 square miles), creating the world's largest network of protected marine areas.

This would help boost declining fish stocks by protecting crucial breeding grounds, he said. Companies caught breaching green zone rules facing a fine of up to A$1.1 million and individuals a maximum A$220,000 penalty.

But the expanded protection area only just meets scientists' estimates and environmentalists' demands that 30 to 50 percent of the World Heritage–listed reef be declared a sanctuary to sustain its long-term health.

Bob Brown, leader of the left-leaning Greens, said the plan needed to be backed up with action on land clearing and global warming, as chemical runoff from cattle grazing, sugarcane growing, and urban development was polluting the reef.

"The federal government, by refusing to act on global warming and land clearing, is undermining and will ultimately overwhelm the work being done by the Great Barrier Reef Marine Park Authority to increase protection for the reef," Brown said.

He warned that coral bleaching was already affecting half the reef and, by 2030, severe bleaching events could happen every year unless global warming was addressed — criticizing the government for refusing to ratify the global Kyoto climate treaty.

Bleaching occurs when heat stresses coral, breaking down its symbiotic relationship with the algae that gives it color and helps it extract nutrients from the sea.

The commercial fishing industry warned the plan could devastate fishing firms and small communities.

"More fishermen will be competing over fewer fish," said Duncan Souter, head of the Queensland Seafood Industry Association.