The Environmental Protection Authority earlier this week said no statistical data was available to prove the scheme has been effective, but retailer compliance has suggested a "significant" decrease in plastic litter.

The controversial scheme was introduced in Tasmania in November 2013, after the state government outlawed the use of regular plastic bags in supermarkets.

The ruling saw Coles and Woolworths supermarkets introduce reusable bags at 15¢ per bag.

"There is no robust data yet available to demonstrate a measurable drop in the contribution of plastic shopping bags to the litter stream, but anecdotal information clearly suggests that the number of plastic shopping bags provided by retailers has reduced significantly," an EPA spokeswoman said.

"Investigations by EPA officers over the past year have confirmed a high level of retailer compliance with the ban on supplying lightweight shopping bags."

Green group, Environment Tasmania, said banning regular plastic bags was a smart move on the government's behalf, but said reusable plastic bags aren't a greener alternative.

"Lightweight bags are the most harmful to the environment and wildlife, but other plastics also last a long time in the environment and we shouldn't leave that mess for future generations to deal with," Environment Tasmania chief executive officer Charlie Sherwin said.

"Tasmania can now aim to become an environmental leader by also reducing the use of heavier weight plastic bags: either by requiring retailers to charge customers for them, as some good businesses already do, or by banning thicker bags up to 60 microns thick, so making biodegradable bags more cost-competitive."

Coles Australia would not comment on the effectiveness of reusable plastic bags, but said its scheme was in full compliance with state law.

Woolworths Australia refused to comment.