was added to a list of cyanobacteria advisories by the state Department of Public Health Friday.
According to DPH, Horn Pond and several other bodies of water—including Wedge Pond in Winchester and Stevens Pond in North Andover—are listed as having signs of cyanobacteria, commonly referred to as blue-green algae.
Officials say that the algae can produce toxins that are harmful to both people and animals.
Animals are not allowed in the water at Horn Pond, according to the city's animal control officer. However, dogs are often allowed in the water by their owners. Health officials say that blue-algae can harm the pooches, according to studies by the World Health Organization.
Blue-green algae tends to form in August and September, according to the DPH.