Commercial fishermen are promising to work with environmentalists to fight a proposal by Seatow to transfer 2.5 million tonnes of West Coast coal a year from barges to ships in Golden Bay.
Port Nelson Fishermen's Association president Darren Guard said there could be "catastrophic effects" on the environment if theproposal went ahead.
Mr Guard said pristine beaches in Golden and Tasman Bays could "turn black" over time from the coal dust blown on the prevailing north to north-west winds.
Coal dust was wetted down in Westport "but the whole town is black regardless".
"Wetting down would not work. The discharge of coal from the wash-down of the barges would be huge over time.
"We will join hands with environmentalists to fight this because we rely on clean water."
Murray Brown, from the Golden Bay Motueka Fishermen's Association, said they were opposed to the idea "at this stage".
Mr Brown said where the barge would anchor was on the edge of a coral area that was protected and closed to trawlers and dredging.
The operation, which would require resource consents from the Tasman District Council, would also interfere with fishing, he said.
"At this stage we are totally opposed until they can come up with a full environmental assessment report and some answers."
Environmentalists have concerns about contamination from ballast water and oil spills.
Seatow director Peter Dunlop said there would be economic benefits for the region.
The Tasman District Council would receive a handling fee and there would be employment, he said .
