A dog that went swimming in the Eel River in eastern Mendocino County died early this month — a death that tests this week confirmed was related to toxic algae, Mendocino County officials said.

It was the second confirmed canine fatality in two months linked to toxic algae and swimming in a North Coast stream. The first case involved a dog that died during an outing on the Russian River.

In the latest case, the stricken dog had been swimming in the Eel River at a Potter Valley-area campground before becoming ill, said Brian Hoy, consumer protection program manager with Mendocino County’s environmental health department.

“It was sick as soon as it came out of the water,” he said. The dog was having seizures and was foaming at the mouth, Hoy said.

He said the owners tried rushing the animal to a veterinary hospital, but before they could get help, the dog succumbed to the deadly, fast-acting neurotoxin — Anatoxin-a — that is found in some types of cyanobacteria, or blue-green algae.

The incident follows a similar canine fatality in late August involving the same toxin in the Russian River in Sonoma County.

Sonoma County officials acted to restrict beach and river access for pets in the aftermath of that dog’s death, which occurred during an outing on the weekend before Labor Day.

Mendocino County officials are not following suit. They instead are advising people to avoid any water body in which they can see the telltale signs of algae growth, including algal scum and mats that can be seen floating in the water or collecting along the shore. It’s not possible to identify which blooms are toxic simply by looking.

Hoy said the county has not tested the water itself.

Extended drought conditions have contributed to an increase in algal blooms, some of which can produce toxins that can be lethal, health officials said. Algal blooms have been proliferating throughout the world, and many scientists believe the spread is related to global warming.

Children and pets are most in danger of becoming ill and should be kept from entering water where algae is present, Hoy said.

Dogs are particularly susceptible because they will drink the water and lick algae from their fur. Children also may inadvertently ingest water while splashing and playing in water, health officials said. Both should be washed with clean water after playing in rivers and other potentially contaminated water bodies, officials said.

Area residents who draw water directly from the river should not drink water that might contain blue-green algae, Hoy said. The toxin is not killed by boiling.

Ingesting the algae can release toxins that can cause a variety of symptoms, including irritation of the eyes, nose, mouth and skin, gastrointestinal symptoms, muscle tremors, seizures and difficulty breathing.

Additional information is available at www.cdph.ca.gov/HealthInfo/environhealth/water/Pages/Bluegreenalgae.aspx.

You can reach Staff Writer Glenda Anderson at 462-6473 or glenda.anderson@pressdemocrat.com. On Twitter @MendoReporter.