The Shooters, Fishers and Farmers party will not negotiate on any legislation with the newly elected New South Wales state government until the Coalition addresses its concerns around the Murray-Darling River, its leader said on Sunday.

The Shooters were the big winners in Saturday’s election, picking up three seats in the state’s lower house and another in the upper house.

It came despite a fiercely fought campaign in which the Coalition rolled out former prime ministers John Howard and Tony Abbott to spearhead an anti-guns campaign following the deadly Christchurch terrorist attacks.

The Coalition said during the campaign it would not do deals with the Shooters, and the stronger-than-expected result for Gladys Berejiklian’s government means she will not need to rely on them to pass legislation in the lower house.

On Sunday, Berejiklian said pointedly said she was “looking forward to working with the three independents” in the lower house (Joe McGirr, Greg Piper and Alex Greenwich).

But the Shooters party leader, Robert Borsak, said he would seek to use the makeup of the crossbench in the upper house to push through its policy agenda.

“They’ve said they won’t come to us, and we won’t support them, so they can deal with the other crossbenchers [in the lower house],” he said.

“We said in the campaign we will not deal with [Berejiklian] and that remains the case, but with [One Nation candidate Mark] Latham getting in, the crossbench has control of the upper house.”

During the campaign the government labelled the Shooters a “fringe” group who wanted to wind back gun laws in the state. The party has long resented the Howard-era gun reforms which underpin NSW firearms laws, but its successful campaigns in the regional seats of Orange, Barwon and Murray were focused on the state’s water supply and health, not guns.

Borsak said the party would not consider supporting the Coalition’s legislation in either house until it addressed its concerns around the Murray-Darling River.

“Fix the Murray-Darling Basin plan, that’s number one on the list,” he said.

The Shooters released a 10-point Murray-Darling management strategy during the election, which includes pausing water buybacks from farmers, establishing a federal royal commission and protecting environmental flows from irrigators.

Borsak said the party would “insist it has to be implemented in full” before supporting other Coalition policy.

NSW Shooters party leader Robert Borsak said he would seek to use the makeup of the crossbench in the upper house to push through its policy agenda. Photograph: Dean Lewins/AAP

He said the party’s other priorities included a freeze on marine park sanctuaries, a “right to farm” bill and a review of the badly managed NSW firearms registry.

The Shooters’ gains in regional NSW were significant but not entirely unexpected – the party has been threatening the Nationals heartland for a number of years. In 2016 Shooters MP Philip Donato won the seat of Orange by 50 votes at a byelection, ending the Nationals’ 69-year stranglehold on the regional electorate.

On Saturday he increased his margin significantly; as of Sunday afternoon he was beating the Nationals candidate on first preferences at all but three polling booths, and picking up 65.5% on two-party-preferred vote.

The party also seems certain to pick up two additional lower house seats from the Nationals in Barwon and Murray, where the Nationals saw their vote drop by 17.8% and 19.8% respectively.

At the Menindee Civic Hall in Barwon, where a number of mass fish kills have occurred in recent months, the Nationals candidate received only seven votes, compared with 130 for the Shooters candidate, Roy Butler.

On Sunday Borsak said the Nationals were “a failed business model”.

“They have for some reason or another sold out their own constituents and I think the issue about water in Menindee is emblematic of what has happened with that party,” he said.

“That issue was central to the campaign in Barwon and that one booth says it all.”

He also took aim at the Coalition’s campaign against the Shooters, accusing the government of putting safety at risk by failing to modernise the firearms registry.

“Howard and Berejiklian’s disgusting scare campaign trying to invoke the massacre in New Zealand as somehow emblematic of us failed dismally and they should hang their heads in shame,” he said.

On Sunday the Nationals leader, John Barilaro, tried to put a positive spin on the result for the party, suggesting the result wasn’t as bad as it could have been.

“You rewind 12 months and two years ago, we were in bother, we could have lost more seats,” he said.

“Yes, there are losses. Yes, it hurts. I hate seeing colleagues lose their jobs, but we are in government and that’s the main game.

“We have to earn the trust back.”

Counting to determine the makeup of the Legislative Council is not expected to be completed for a number of days.