There are elevated levels of a toxic substance that could be deadly to dogs and harmful to people in two lakes in Montgomery County, Maryland, officials say.
Blue-green algae released the toxin microcystin in Lake Needwood and Lake Frank in Rock Creek Regional Park.
If ingested, microcystin can cause liver damage to people and pets.
The toxin often appears at the lakes during the summer.
"An algal bloom toxicity can be very dangerous and possibly lethal if not treated when clinical signs start occurring," Dr. Matthew Antokowiak, a veterinarian at AtlasVet in Washington, D.C., previously told News4 in 2017.
Montgomery Parks said in a statement Tuesday that pet owners should keep their dogs on leashes and not allow them to drink or come into contact with the water.
"When you are near a body of water and are tempted to let your dog go swimming, if you notice anything weird, slimy, gross or unusual floating in the water, it would be better for both you and your pet to stay on dry land,” Antokowiak said.
Signs that a dog has been affected include excessive drooling, panting, fainting, vomiting and seizures.
People are prohibited from swimming at the lakes, but boating and fishing are allowed.
Montgomery Parks said to avoid direct contact with the water and "only eat properly cooked muscle meat of fish that are caught in the lake."
Pollutants usually cause algal blooms, including fertilizers from homes and farms, Montgomery County natural resource specialist Matt Harper said in 2017. Warnings about algal blooms in the two Maryland lakes have been issued since 2009, he said.
Algae grows in the lakes year-round. In the summer months, the lakes get more direct sunlight and warmth. These, coupled with pollutants in stormwater runoff, create “the perfect storm” for algae growth, Harper said.
The algae lets off microcystin, which Montgomery Parks monitors. If microcystin is measured at more than 10 parts per billion, it has potential health risks, and the department issues warnings.
Once increased levels of microcystin are detected, there’s not much officials can do to stop it.
Better management of stormwater could potentially prevent future algal blooms, Harper said.
“I would definitely not hesitate to still use [them],” Harper said.
Still, visitors are advised to wash their hands thoroughly after being in or near the lakes.
Montgomery Parks said it will continue to monitor the lakes and update the signs when the warning is lifted.