Security guards have begun patrolling the reservoir to stop people from climbing down onto the muddy reservoir floor.
Jersey Water last week hired the security firm G4S to protect the site following reports to the company that some people had been riding mountain bikes on the drained reservoir and allowing their dogs to wade into the mud.
Signs have also been erected to warn people of the dangers of entering the reservoir at Grouville, which is currently just 35 per cent full.
