A pond in South Portland’s Hinckley Park has tested positive for a type of algae that produces toxins that can be fatal for dogs.

The South Portland Parks and Recreation Department issued a warning Thursday evening after testing results showed a blue-green algae bloom could possibly produce toxins harmful to dogs.

“We are asking that people please keep your dogs away from the shorelines. Don’t let them drink the water, swim or go near the algae that is accumulating on the shorelines,” the department wrote on Facebook.

The city will post signs around the pond to warn dog owners to keep their dogs away from the water.

At least four dogs have died this summer in North Carolina and Georgia after swimming in water contaminated with blue-green algae, according to the Associated Press.

Blue-green algae growth, known as cyanobacteria, is made up of microscopic organisms that naturally occur in streams and lakes. Much of it is harmless, but it can produce toxic chemicals that cause sickness in people and can be fatal to dogs.

Blooms of blue-green algae have been documented in all 50 states, David G. Schmale III, a professor at Virginia Tech, told CNN.