Fish and Game says if the allegations of South Canterbury farmers attempting to falsify river levels to get around water restrictions are true, they should be prosecuted.
The Canterbury Regional Council is investigating a claim that local farmers were spotted building a weir around a water metre in the Pareora River, south of Timaru.
The council launched its investigation after receiving a complaint.
Fish and Game's chief executive Bryce Johnson said if the complaint stacked up, the farmers should be charged.
"The whole idea of setting minimum flows is to protect in-stream values, you know farmers don't have a mortgage over nature, it really sits with the public. These people are exercising a privilege to use water for irrigation and of course minimum flows are set to protect in stream values and it seems these people are simply rejecting that and are just looking after their own interests at the expense of nature," he said.
Mr Johnson said he had never heard of that happening before.