A $444 million lump-sum payment to the Great Barrier Reef Foundation was "pretty good common sense" to help the reef, Prime Minister Scott Morrison says.
Mr Morrison has taken responsibility for the coalition's controversial decision, which has been subject to months of scrutiny since it emerged there was no tender process for the record grant.
The money was also handed over in one financial year rather than spread over the budget's four years.
Former treasurer Mr Morrison said he and Finance Minister Mathias Cormann invested in the reef in one go so the budget would not be impaired in the long run.
"We took the right financial decision when it was brought to us that the environment minister at the time, Josh Frydenberg, wanted to make this investment in the reef," he told reporters in Perth on Monday.
"It seemed to me like pretty good common sense in how to manage the finances and ensuring that is now in place to support these projects into the future."
But Labor's environment spokesman Anthony Albanese accused the prime minister of using the grant to make the budget look better.
"He ... doesn't get how important good economic policy is and good fiscal policy, because this one-off payment in order to fiddle the budget figures is not justifiable," he told reporters in Sydney on Monday.
The charity's chairman John Schubert told a Senate inquiry last month he was unaware the foundation would be receiving the money until a meeting with former prime minister Malcolm Turnbull and Mr Frydenberg in April.
The foundation told the inquiry it has projects due to start next year.
