PORTLAND (AP) — Scientists know what caused the ocean foam that has killed thousands of seabirds in Oregon and Washington, but they don’t know exactly why it suddenly showed up in such deadly abundance off the Northwest coast.

The organism is a single-cell phytoplankton, or algae, called Akashiwo sanguinea.

It has been blamed for red tides off Japan, Australia, New Zealand, Brazil and Hong Kong.

In mid-September, it began multiplying in an algae bloom off Washington’s Olympic Peninsula. The algae has turned up in Washington’s Puget Sound before, and in 2001, it was detected off Newport. But this time it’s killing Northwest seabirds.

While algae blooms are common in the Northwest, and essential to providing food that supports fisheries, this algae created surfactants — detergent-like substances that covered seabirds in foam and stripped away their waterproofing, causing them to become hypothermic and die.

Thousands of dead and dying birds washed up on beaches in mid-September around Kalaloch on the Olympic Peninsula. Last week, scores more washed ashore on Washington’s Long Beach Peninsula, just north of the Columbia River, and as far south as Cannon Beach.

Hundreds of birds have been sent to West Coast care facilities for cleaning and feeding. They include Western grebes, common murres, red-throated loons and common loons.

Why now?

“This is the big million-dollar question,” said Michelle Wood, a phytoplankton specialist at the University of Oregon.

The organism flourishes in warm, stratified water. That’s ocean water with a warm layer on top.

Last week, the ocean was warmer than usual.

Sensors 10 miles from Newport detected an ocean temperature of about 55 degrees. That’s about 5 degrees higher than averages from 2002 to 2008 at the same spot at the same time of year, said Pete Strutton, an Oregon State University associate professor of oceanography.

Strutton also noticed another phenomenon in the ocean around Oct. 14 — as water temperatures rose, the salinity dropped — and this algae thrives in warm water with low salinity.

He suspects that recent storms helped create the perfect conditions.

The bloom that created the killer foam is at least seven weeks old, but appears to be less of a problem now with strong winds coming from the north.

“I’m guessing that with these high winds that it’s been pushed offshore,” said Bill Peterson, an oceanographer with the fisheries service in the National Oceanic and Atmospheric Administration.

Zachary Forster, phytoplankton specialist at the Oregon Department of Fish and Wildlife, saw fewer dead and dying birds on Wednesday on Clatsop County beaches and less foam.

Julia Parrish, a University of Washington marine biologist and professor, hopes for the day when scientists might at least be able to predict such a bloom.

Still, “we will probably never have the ability to prevent the bloom,” she said.