A farmer at the centre of the Menindee fish kill story has lodged a complaint with police, alleging he felt "intimidated" by a staff member of lobby group Cotton Australia.

The owner of far western New South Wales property Tolarno Station, Rob McBride, has filed the complaint with New South Wales Police.

Intimidation is an offence under the New South Wales Crimes Act.

Police are now investigating whether there is evidence of any offence and are interviewing other witnesses.

In the official police complaint, seen by the ABC, Mr McBride alleged that a Cotton Australia employee "threatened" him.

Menindee grazier Rob McBride has filed a complaint with police alleging that he was "threatened" by a Cotton Australia employee. ( ABC 7.30 )

Cotton Australia has released a statement saying the claims "are entirely denied".

Mr McBride has been front and centre of the debate over water use in the Darling River.

In January he appeared in a video holding up dead Murray Cod after a mass fish kill outside Menindee.

The footage was a viral sensation and is credited with bringing international attention to the state of the Murray-Darling Basin.

Mr McBride has strongly criticised the growth of the cotton industry upstream in the Darling River and its impact on the water available for his community.

The complaint

Mr McBride's complaint to relates to a public event in Sydney on February 23 at the University of New South Wales.

The University's Global Water Institute hosted the event, The Future of the Murray-Darling, and estimated more than 100 people attended.

Cotton Australia representatives were allowed to attend but their request to have a spokesperson address the group was knocked back, organisers said individual growers could speak but not the organisation itself.

According to Mr McBride's signed witness statement, a Cotton Australia employee approached him at the conclusion of the forum and made the following comment:

"Unless you stop your Facebook page, the Cotton Industry will unite throughout Australia and crush and destroy your family, your business and Tolarno Station."

Lower Darling River farmer Robert McBride shows the dry river bed of the Lower Darling River in 2016. ( Supplied: Rob McBride's YouTube video. )

Mr McBride's statement also makes reference to a separate conversation he was not present for.

He wrote that New South Wales Independent MP Jeremy Buckingham and his media advisor Max Phillips both heard the same employee make a statement similar to "Cotton Australia is at war with the McBride family at Tolarno Station".

Mr McBride alleged the two comments made him "feel sincerely threatened".

"I feel my family's welfare has been threatened," Mr McBride told police.

"I also feel [the employee] has directly threatened my company."

Cotton Australia denies all allegations

Cotton Australia chief executive Adam Kay in 2017. ( ABC News: Dominique Schwartz )

As previously stated, Cotton Australia maintained that Mr McBride's claims are "entirely denied".

Cotton Australia further said Tolarno Station and Mr McBride have not "approached Cotton Australia about the matter".

"Similarly NSW Police have not approached Cotton Australia or any of its employees," the statement from the organisation said.

"In the circumstances it would be inappropriate to comment further at this time."

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A spokeswoman for NSW Police confirmed officers are making further inquiries.

"Police from Eastern Beaches PAC are investigating the matter," she said.

Jeremy Buckingham and his media advisor Max Phillips have both provided statutory declarations to the ABC outlining their recollections of their contact with the Cotton Australia employee.

Mr Buckingham said his "contemporaneous note" stated that they said to him:

"We will go to war with the McBrides. We don't want war with the McBrides. You are in a position to broker an end the conflict."

Mr Buckingham said they went on to ask whether he would "be prepared to do a video supporting cotton".

Mr Buckingham said the CEO of Cotton Australia Adam Kay was present for the conversation.

Max Phillips also provided the ABC with his recollection of the comments that were made to Mr Buckingham.

"We will go to war with the McBrides. "We don't want to go to war with the McBrides. "You [meaning Jeremy Buckingham] are in a position to intervene and stop us going to war with the McBrides [by stopping the targeting of cotton as a cause of the problems in the Murray Darling]. "You can step in to ensure we don't have to go to war with the McBrides."

Jeremy Buckingham appeared in one of the January videos at Menindee with Mr McBride, in which the politician declared the stench of dead fish was making him unwell and moved off screen and could be heard retching.

Water debate heats up

The uproar over the deaths of millions of fish at Menindee led to public rallies about water shortages and questions about upstream irrigation, particularly focused on water usage in the cotton industry.

The debate over the basin has been increasingly heated over recent months.

A number of politicians who travelled to Menindee following the fish kill had police escorts.

NSW Regional Water Minister Niall Blair said he had faced threats after the mass deaths of the fish, and in one instance avoided angry protesters as a security precaution when he went to the community.

Cotton farmers have also reported online abuse and threats.

In his statement to police Mr McBride said that over the past decade there has been "continuous conflict between my company and the cotton industries regarding the upkeep of the Darling River".