Commonwealth funding to arrest declining water quality on the Great Barrier Reef has dropped by more than $11 million a year, internal government figures suggest, despite growing concerns over threats to the reef.

The figures have emerged weeks out from the federal budget, which critics last year said ignored the coral bleaching crisis that has severely damaged the reef, as well as other environmental problems that are expected to hurt tourism and jobs.

Federal government funding to improve reef water quality has declined, figures show.

Flight Centre founder Graham Turner said more Commonwealth funding is needed to protect the reef, and former government official Adam Smith said current funding levels were “probably not adequate”.

After climate change, poor water quality is the most pressing problem facing the reef. It is largely caused by nutrient, pesticide and sediment run-off from agriculture and coastal development. It can cause algal growth at the expense of coral, block light and smother corals, as well as exacerbate outbreaks of the venomous crown-of-thorns starfish, which are a major cause of coral loss.