The federal opposition and environmentalists are decrying new figures that show more than half a million hectares of forest was cleared in the Great Barrier Reef catchments over four years.

The government figures show shows that 596,000 hectares of forest was cleared between 1 July 2012 and 30 June 2016.  That's an area more than twice the size of the Australian Capital Territory.  But the total picture might be even worse, because the figure doesn't include land that is not classified as forest, such as sub-forest woody vegetation.

Land-clearing and deforestation cause more sediment and nutrient runoff into the reef, which stimulates algae growth which can smother corals.  It's the second biggest threat faced by Australia's natural wonder, following global warming.

"It's a destruction of habitat and a disaster for the Great Barrier Reef," said Labor's environment spokesman Tony Burke as quoted by The Guardian.  "The Liberal party seems to think that they can turn a blind eye to the destruction of the environment and runoff into the Great Barrier Reef and then throw money to private organisations and pretend that the vandalism never occurred."

Billions of dollars has been spent to improve water quality at the reef, but the Greens say the situation won't improve until land clearing stops and stronger environmental laws are passed and come into force.

"We need to do a lot better with regards to controlling land clearing," said Andrew Bartlett, the Greens’ environment and biodiversity spokesman.  "Those figures are staggering and it shows both the need to strengthen the existing laws federally and better enforce what’s already there," he added, "We're already on record wanting strong improvements in this area, but these figures show it's all the more urgent."

The Guardian says it sought a response from the government, but environment minister Josh Frydenberg is overseas and assistant environment minister Melissa Price did not respond.