More than a thousand protestors on land and water have crowded Sullivan's Cove to protest Tassal's Oakehampton Bay fish farm proposal.
The aquaculture giant is waiting only on Commonwealth approval for a 28-pen facility, housing up to 80,000 fish.
Laura Kelly from Environment Tasmania said people won't stand for 'trashing of our valuable coastline'.
"This is people from all walks of life in Tasmania and what unites them is their passionate love for the ocean and their belief that Tassie can be clean and clever," Ms Kelly said.
Tassal issued a statement, saying it respects people's right to protest but stresses strict guidelines are in place to ensure the proposed salmon farm has 'critical environmental protection programs'.
The statement says the company is committed to positive outcomes for both the community and the business.
Deputy Premier and Primary Industries Minister Jeremy Rockliff posted a video on social media after the protest, pointing to the government's blueprint for the industry.
"What we are doing is working with the Tasmanian community and the industry to develop a sustainable industry growth plan," Mr Rockliff said.