A government MP has been caught joking with the head of the Murray-Darling Basin Authority about who’s had a worse week, before quipping that the basin plan took 100 years to make but “one night to fuck it up”.

Microphones picked up the conversation between Liberal MP Tony Pasin and the chief executive of the MDBA, Phillip Glyde, just before Glyde was due to give evidence to a Senate inquiry into regional development and decentralisation in Canberra.

Pasin, a South Australian backbencher, was recorded jokingly comparing the misfortunes of the government and the MDBA this week.

“I was about to say we’ve probably had better weeks than you’ve had, but I’m not sure that that’s right,” Pasin says.

Glyde responds: “No this is just a normal week, it’s always controversial.”

Pasin, who regularly speaks on water issues for South Australians, replies: “Nice try Phil, it’s more than another week.”

The basin plan – a vital water-sharing agreement underpinning the management of the entire river system – is at serious risk, after New South Wales and Victoria threatened to walk away this week.

Glyde is recorded saying that it’s been 101 years almost to the day since the MDBA’s predecessor held its first meeting.

Pasin replies: “Yeah I know … I was about to say it took 100 years to get to this point, it took us one night to fuck it up, but anyway…”

The MDBA is facing a mutiny from two key state governments, NSW and Victoria, that are furious over the blocking of changes to the basin plan in the Senate on Wednesday night.

The changes, part of the northern basin review, would have reduced the amount of water returned to the environment in northern NSW and Queensland.

But Labor and the Greens combined to move a disallowance motion in the Senate, which effectively killed off the changes.

Pasin told Guardian Australia that when he said “us” on Friday, he was referring to federal parliament.

“All those who supported the Greens motion in the Senate this week have put the plan in jeopardy,” Pasin said.

“As the member for Barker, I represent the largest section of the river in South Australia. As such, I am extremely disappointed and frustrated that Labor, the Greens, others on the crossbench have put us in this situation.”

“It took us 100 years to get to this point and by playing politics they have potentially blown up the plan that my constituents along the river are banking on.”

The NSW regional water minister, Niall Blair, said walking away from the plan would free the state government from the “whim of politicking from federal Labor, the Greens and the South Australians fighting for votes”.

“Our stance is about securing the future of western NSW – the Labor party seems more concerned about its electoral prospects in South Australia,” Blair said on Thursday. “It is federal Labor and the Greens in the Senate who have brought the Murray-Darling basin plan to the brink of collapse.”

The federal government, through its water minister, David Littleproud, is attempting to broker an agreement and save the basin plan. Victoria and NSW have urged the commonwealth to do what it can to fix the “Senate’s mess”.

This week, Pasin told South Australian radio the government was doing all it could.

“We will try our guts out to make sure this plan is implemented in full and on time,” Pasin said.