A group of NSW farmers want to sell their water licences to people who will not grow cotton.

Concern about the condition of Murray-Darling rivers and the effects of drought and water allocations are growing.

Criticism of farmers has grown alongside that concern, with many blaming growers for overusing or misusing allocation.

With more than 30,000 megalitres of irrigation water entitlements up for grabs, a group of anonymous farmers has allowed CBRE group - a commercial real estate firm - to broker a deal.

“The vendors are motivated to sell by the growing commentary around the degradation of the Barwon-Darling river system,” Danny Thomas, regional director of CBRE Agribusiness, has told the ABC.

“There are also allegations that irrigators are at least partly responsible for the problems in the system.”

Much of the Barwon-Darling system’s water is classified as Class B, which requires a minimum water flow in the river before it can be pumped.

There are around four farming families are involved in selling licences.

“The families have been observing commentary about the reasons for the river been in the state that it's in,” Mr Thomas said.

“Some of the commentary says people like them are part of the problem, and those that want to proactively return water to the river have an opportunity to do so now.”

Insiders say it is unusual for farmers to sell water entitlements collectively.

“The opportunity is there for people to buy the licenses at a level of value which incentivises the growers not to grow cotton,” Mr Thomas said.