The warning comes after several alerts were issued for Hemlington Lake in recent weeks, with visitors advised about the presence of potentially toxic algae in the water. Several warnings have been released for suspected cases of toxic algae in Hemlington Lake, Middlesbrough, over the last six weeks. Blue-green algae can often be identified by a bright green, paint-like appearance on the surface of water. Owners are being advised to keep dogs on leads if blue-green algae has been spotted and to avoid letting pets enter affected water. "If you suspect your dog has come into contact with blue-green algae, contact a vet immediately, even if symptoms seem mild at first.