Potentially toxic algae found at Guernsey's main reservoir

Saturday 07 July 2018

Guernsey Water is investigating the discovery of algal bloom at St Saviour’s Reservoir which can be toxic to humans and animals.

Routine monitoring found there was blue-green algae present in the water, but there are treatment processes to remove it meaning there are no adverse effects on the island's drinking water supplies.

As a precautionary measure, notices have been posted next to the reservoir warning that contact with the algal scum should be avoided. Those who fish in the reservoir have also been told.

Guernsey Water has said that while blue-green algae exists in fresh waters throughout the world, they are only noticed "when their populations increase to form ‘blooms’ and when they form scums – looking like blue-green paint, or when they collect along the shore line."

This is more likely to occur after long periods of hot, sunny weather like we have recently experienced.

Any adverse health effects which are possible, but do not always occur, will include skin rashes, eye irritations, vomiting and diarrhoea. Toxic algae have caused death in livestock and pets so it is best to avoid it if possible.

Guernsey Water said the "level of toxicity can fluctuate, it can appear one day, be dispersed by the wind and mixing and re-accumulate at any time."

The utility firm said it monitors algae levels in all its raw water sources so treatment processes for drinking water can be launched immediately to remove the blue-green algae from supplies.