WHITE CITY — Whetstone Pond is overrun with a pudding-like, potentially toxic algae bloom that has not previously been reported to state health officials anywhere in Oregon.

The bloom of aphanocapsa, which has been present at the Denman Wildlife Area for the past two years, has taken over about 30 percent of the 5-acre pond and created a crusty mat that has choked an irrigation pipe at its east end off East Gregory Road.

It is different than the more common anabaena flos-aquae strain found annually in some area reservoirs and in Whetstone Pond as recently as 2010.

"It's a species I haven't even heard of before," said Rebecca Hillwig, a natural resource specialist with the Oregon Health Authority, which keeps tabs on harmful algae blooms in Oregon.

"I haven't seen a report on it here," Hillwig said. "Even in our archives I haven't seen that species here."

Aphanocapsa can produce toxins that are potentially deadly to people and pets throughout its life cycle, with toxins most likely associated with bloom die-offs, but the cyanobacteria can also "leak" toxins throughout its lifetime, Hillwig said.

Hillwig has requested a water sample from Whetstone to determine whether the cell counts eclipse the 100,000 parts per mililiter needed to trigger a public health advisory.

Until then, people and pets should avoid water contact, don't ingest water from the pond, and practice catch-and-release fishing, Hillwig said.

One of the few still-water angling locations on the Rogue Valley floor, the shallow pond draws about 100 carloads of visitors a week, Denman records show.

Originally misidentified as a nontoxic algae called nostoc, it was positively identified this past week by an algae specialist at Portland State University's Center for Lakes and Reservoirs, said Clayton Barber, who manages the wildlife area owned by the Oregon Department of Fish and Wildlife.

Barber said it has been there at least two years and appeared to have died off the past two winters. However, it appears the heavy balls of scum simply sank, Barber said.

"It's a big, pudding-like scum that goes all the way to the bottom," Barber said. "It's getting more and more prominent each year. It's growing."

Wind has blown higher concentrations of it to the pond's east end, where it has encrusted enough in the hot sun for birds to walk on it.

"It's so crusty it makes noise when you hit it," Barber said while tapping it with a net.

The source of the algae is unknown, and no trace of it appeared during the last sampling of pond water tested by health officials in 2010, Hillwig said.

The pond was created in the 1950s by damming Whetstone Creek, which drains large swaths of the White City Industrial Area, which has had myriad instances of industrial contaminants being leaked into it, according to the state Department of Environmental Quality.

A Rogue Valley Sewer Services survey found high levels of phosphorus in the creek, Barber said. Phosphorus loads are often associated with algae blooms.

ODFW will consider short-term use of herbicides to kill off the algae, with possible long-term solutions to include removing the sediments that have built up over the decades and deepening the pond, Barber said.

Barber said surveys of other wildlife-area ponds have not shown any signs of aphanocapsa.

While no public health warning or advisory has been issued at Whetstone, wildlife-area workers have erected signs warning of the blue-green algae's presence.

During advisories, people and pets are warned to avoid all water contact, but compliance is voluntary. Anglers are encouraged to practice catch-and-release fishing during advisories.

Toxins cannot be filtered by standard camp filters or by boiling the water. In-home filtering systems cannot cleanse the water, though public treatment plants can reduce algae toxins through filtration and disinfection.

People who eat fish from algae-tainted waters should remove all fat, skin and organs before cooking because toxins can collect there. People should not eat crayfish or freshwater shellfish taken from infested lakes during an advisory.

No confirmed human illnesses have been tied directly to an algae outbreak in Oregon. However, at least four dogs have died in past years from toxins in water near the Umpqua River near Elkton.

— Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or mfreeman@mailtribune.com. Follow him on Twitter at www.twitter.com/MTwriterFreeman.