In Wewak a group called 'Project Sepik', says the Papua New Guinea government should say "no" to the proposed Frieda River mining project.
The East Sepik civil society group said there had been inadequate environmental impact statements conducted.
The copper and gold mine was being planned by an Australian-registered, but Chinese government -owned company, called PanAust.
Project Sepik made the call after the views of 10 independent experts on the impact statement went to PNG's Conservation and Environmental Protection Authority.
The expert reports were sought by Project Sepik in collaboration with the PNG legal advocacy group, the Centre for Environmental Law & Community Rights.
They noted the developers of the Frieda project could not show mine waste could be stored in such a way that the Frieda River wouldn't be damaged.
They also noted that, given the development would be in a seismically active area and subject to extreme rainfall, a ruptured tailings dam could cause catastrophic damage.
In addition they said there was no evidence that free, prior and informed consent had been given by all of the landowners - something they note is essential for an environmental impact assessment.
And the impact assessments didn't include the information necessary to show that a comprehensive analysis was done.
This included details about the operation and closure of the mine, an assessment of the proposed airport, and a resettlement plan for the 4 villages requiring relocation.
"The 100,000 people who live on the Sepik don't want this mine," said Emmanuel Peni, the co-ordinator of Project Sepik.
"It will not bring the promised benefits to my people and it will endanger the beautiful Sepik river, which provides us not only with our home but our livelihood and also defines our identity."
Project Sepik's push came as it joined with two Australian NGOs, Jubilee Australia and Aidwatch, in launching a campaign called "Save the Sepik."
Jubilee Australia's Luke Fletcher referenced the OK Tedi disaster saying they were still tracking the ongoing tailings disaster in Bougainville.
"In both cases the tailings released into these rivers contaminated and killed fish, caused mass flooding and the spread of contaminated mud, decimated land previously used for growing food and led to the leaching of heavy metals in a chemical process called acid rock drainage," Mr Fletcher said.
"The Australian-sanctioned destruction of PNG's natural environment must end now with the rejection of PanAust's irresponsible plans for the Sepik."
Natalie Lowrey, the co-ordinator of Aidwatch said the Sepik region was a haven of biodiversity and home to some of PNG's rarest plants and animals.
"It is the largest unpolluted freshwater system in Papua New Guinea and one of the largest and most intact freshwater basins in the Asia Pacific.
"Yet if the mine were to go ahead, the region could face catastrophic and permanent destruction," Ms Lowrey claimed.
Comment on the call made by the NGOs was sought from the company by RNZ Pacific, but there has been no response to date.