Fish & Game has accused the government of mounting a "sneaky backdoor attack" on one of the core principles of New Zealand's cornerstone environment laws.
The organisation says the attack is hidden in the fine detail of the government's proposed changes to the National Policy Statement for Freshwater Management.
It had commissioned lawyers Sir Geoffrey Palmer QC and Elana Geddis to scrutinise the proposed amendments, chief executive Brian Johnson saying their analysis was deeply worrying.
"What has been revealed is a sneaky backdoor attack on one of the core principles of the Resource Management Act, which will effectively put economic growth ahead of the environment," he said.
The public should be worried about what the government was planning for the environment and the "cherished" rivers and streams where they swim, fish and gather food.
"When you have two such highly-respected legal experts as Sir Geoffrey and Elana Geddis warning of the environmental dangers hidden in the proposed amendments, then it's time to sit up and take notice," he said.
"With the conflicting responsibilities regional councils already have for environmental protection and regional development, you don't have to be a political scientist to see the environment will be the loser if the economy is elevated.
"This is deeply concerning as 'economic well-being' and 'productive economic opportunities' are limitless, and lend themselves to political abuse.".
The public needed to be aware of this "crafty attempt" to firmly place the economy and big business ahead of the environment would mean, including significantly undermining the degree of environmental protection that was currently provided by the existing freshwater policy guidelines.
"The changes will effectively undermine the environmental protection in the existing freshwater policy statement by requiring 'economic well-being' and 'productive economic opportunities' to be given the same status as the environment," he added.
"The New Zealand public is growing increasingly angry about the state of their rivers, lakes and streams. They have protested, signed petitions and marched on Parliament, yet the government is brazenly trying to ignore them and pretend it has the best interests of the environment at heart.
"The simple fact is we cannot go on abusing the environment in the way we have. The government has to realise it is finite, not limitless."
The proposed amendments to the national policy statement have widespread criticism, environmentalists accusing the government of trying to shift the goalposts to allow dirtier water to be classed as swimmable.
Expert freshwater scientists have described the suggested guidelines as confusing, complicated and difficult to understand.
Mr Johnson said everyone who cared about the environment must take a stand and tell the government they are fed up.