Mussel harvesting remains prohibited in the majority of production sites around the isles.
The Shetland Times has learned only one of 20 designated areas has been given the all clear to resume farming after a lengthy hold-up this summer.
Early last month the council’s environmental health department ordered harvesting of mussels from all 80 sites be halted.
The order came after high levels of the naturally-occurring phytoplankton were detected during routine tests.
The organism was the cause in July of an outbreak of diarrhetic shellfish poisoning, which brought unpleasant consequences to 70 people who ate infected Shetland mussels in the south east of England.
Routine testing has been continuing at all of Shetland’s production areas since the order was imposed. Two consecutive samples below the regulatory limit must be recorded in each site before they can resume production.
Producers have been left frustrated by the tediously high levels of phytoplankton which have remained. Earlier this month one site was allowed to open but was later closed again when the organism was detected.
The area, or “pod”, that has opened is in the Cliffsound near Quarff and Trondra, which includes seven sites.
Blueshell Mussels, and a number of other producers, operate from there.