Argyll and Bute Council is warning about raised levels of naturally-occurring algal toxins at a number of lochs in the area.
Now harvesting at the sites has been halted to allow levels to fall.
Members of the public are advised to avoid eating shellfish from the areas.
The naturally occurring toxins accumulate in shellfish such as cockles, mussels, oysters or razor clams.
When levels reach certain limits, harvesting of the affected species is prohibited, as consumption can pose a health risk.
Warning notices for the public and casual gatherers have been posted at various locations on the shore.
Commercial shellfish harvesters in the affected areas have been contacted by the council, with steps taken to postpone harvesting until algae levels subside.
The areas currently closed for harvesting are: Ardcastle Bay, Stonefield Bay and Ardkinglas at Loch Fyne; Loch Striven; Kilbrannan Sound, Kildalloig Bay, Carradale Bay, Saddell Bay.
However, some parts of Loch Fyne closed previously have now been reopened, including Otter Point, Balliemore, Stonefield.