Algae outbreak forces swimming ban; municipal water deemed safe

Marion Reservoir’s Cottonwood Point beach is closed until further notice because of the reappearance of blue-green algae that can produce a toxic, potentially lethal neurotoxin.

The World Health Organization regards a concentration of 20,000 cyanobacterial cells in a water sample as a health risk.

According to park ranger Neil Whitaker, samples from the swimming beach this week found nearly 36,000 cyanobacteria.

If the concentration exceeds 50,000, Whitaker said, all other forms of recreation involving contact with water will be halted.

No-swimming signs were posted Thursday, and pamphlets were being distributed Friday, warning visitors not to drink untreated water from the reservoir.

The reservoir is the source of drinking water for Marion, Hillsboro and Peabody, but the Corps and city officials in Marion and Hillsboro, which treats water to Peabody, emphasized that municipal drinking water remained safe.

“It doesn’t change anything,” Marion Administrator David Mayfield said.

He misspoke, crediting the Marion plant’s ozone treatment, which actually would make the situation worse. In fact, its activated carbon filtration is what gets rid of the toxin.

Hillsboro’s water plant is similarly prepared.

“We’ve been pretty successful treating water as it comes from the lake,” Hillsboro Administrator Larry Paine said. “It’s a challenge, but we’re doing well. We don’t expect to change the treatment process.”

Other areas at the reservoir with blue-green algae concentrations were Marion Cove, 8,522; French Creek Cove, 7,162; overlook, 2,190; dam, 1,799; and Hillsboro Cove, 517.

Blue-green algae initially is dark green and often is not visible to the naked eye. Toxins are not released until algae blooms die — which is why ozone treatment actually makes matters worse, because it kills the algae.

Swimming in an area with a moderate concentration of algae may result in a skin rash and itching. Ingestion of water with a high concentration of algae may result in serious illness or death for both humans and animals.

Pound for pound, the algae toxin is more potent than cobra or rattlesnake venom, cyanide, or arsenic.

According to the information distributed by the U.S. Corps of Engineers, there is no feasible way to treat or control algae blooms, but in time, the blooms will subside.

An outbreak of blue-green algae in 2003 caused both Marion and Hillsboro to stop processing reservoir water. Both have upgraded their water treatment processes to include carbon filtration since then.

Beaches were closed briefly in 2004 for what was termed a more severe outbreak. A similar scare occurred in 2007, but drinking water was not affected because of newly installed carbon filtration.

Blooms have been linked to excessive use of phosphorous or nitrogen, either in agricultural or landscaping activities. Wet weather following a protected dry period also has been associated with blooms.

Water was released from the reservoir Thursday because the level had risen more than two feet.