The company has decided to break from standard practices ingrained in the worldwide industry and ditch the nets over concerns about contamination.

Tassal's head of sustainability Linda Sams said the company had been working to remove the nets since 2011.

"We saw copper as an unnecessary, unnatural material going into the marine environment, which we had in our power to stop using," Ms Sams said.

"The copper could flake off and at high levels it can be toxic to crustaceans, invertebrates and other sea creatures."

The last of the company's copper-treated nets was removed from a fish farm in the Dover region.

Ms Sams said Tassal had spent $18 million removing the copper-coated nets and rolling out new, plastic nets the company believes will be better for the environment.

"These semi-rigid, smooth plastic nets are strong and difficult for seals and diving birds to breach," she said.

"They don't foul easily and they're straightforward to clean, which also saves the company on labour costs."

Ms Sams said more than 100 Kikko poly- monofilament nets were now being used at Tassal salmon farms in the Huon, Dover and Tasman regions.

She said Kikko nets accounted for about 60 per cent of Tassal's netting.

The company is expected to spend between $5 million and $10 million to phase out non-treated, traditional nets still in use around the state.

Ms Sams said with the netting initiative well under way, the company's attention would now turn to implementing sustainability initiatives at its processing facilities.

Tassal operates three processing facilities, two salmon hatcheries, two retail outlets and marine farms in six Tasmanian regions.