More shellfish growing areas are closed than ever before in Tasmania due to algal blooms, according to industry leaders.

Key points: Toxin-producing algae in south and south east make wild shellfish unsafe to eat

Toxin-producing algae in south and south east make wild shellfish unsafe to eat Two types of toxin have been detected – one causes paralysis, the other diarrhoea

Two types of toxin have been detected – one causes paralysis, the other diarrhoea Cooking does not destroy the toxins

Ten growing areas have been shut down because of toxic algae, extending from St Helens down the east coast to Frederick Henry Bay in the south east and Dover in the south.

No wild shellfish should be collected from the affected regions.

More than 50 producers cannot sell or harvest their produce and have to wait for two clean results before they can re-start operations.

Bruny Island remains one of the few areas unaffected.

Two of the state's biggest players Shellfish Culture at Cremorne and Spring Bay Seafood Triabunna are also free to trade.

Algal blooms hit much of Tasmanian industry

Oysters Tasmania CEO Neil Stump said algal blooms, which emerged as issue in 2012, appear to be getting worse.

"A fairly large part of the Tasmanian industry is currently closed," he said.

"Industry has started to adapt to work around these closures but it does have an impact on cash flow."

He said it was hard to determine the financial loss to the sector, in part because in winter seafood sales drop.

Mr Stump said the industry was relatively in the dark as to why the blooms occur, with rising water temperature one possible factor.

"There is currently research underway to provide us with greater understanding," he said.

"We're still in the process of trying to understand the environmental drivers that accompany these algal blooms and it does vary from area to area."

For some oyster growers it's a double blow with many of the affected areas also devastated by Pacific Oyster Mortality Syndrome (POMS) earlier in the year.

The Smithton growing area is also closed due to water quality issues rather than algae.

Warning not to eat wild shellfish

The Tasmanian Government has warned residents who cook and eat wild shellfish from the east coast risk serious illness.

Acting Public Health director Dr Mark Veitch said two types of shellfish toxin have been detected - one causing paralysis, the other diarrhoea.

"Shellfish feed on algae and concentrate the toxin," he said.

"This makes them dangerous to eat and may cause serious and even fatal illness."

The shellfish include wild oysters, mussels, clams pipis and scallops.