The plankton known as pseudo-nitzschia is microscopic. In a picture magnified 300 times, the plankton is semi-transparent with yellow streaks. There is no way to tell by microscopic examination if it toxic or harmless. That takes chemical analysis.

The toxic examination of this cloud shows it is highly toxic.

Dr Rita Horner says the numbers in the cloud are staggering: "If you can think of 11 million, even small, things in a quart of water, that's an awful lot of cells."

That's what scientists on the research vessel found: 11 million toxic cells in a liter of water.

The danger is, it'll drift southward and toward land, winding up in our state's oyster and clam beds. Even at 200 cells per liter, it would be considered dangerous.

In 1997 and 1998, coastal shellfish farms lost half of their crop in one toxic bloom from late November through December.

The threat is huge. The annual shellfish catch on the West Coast is worth $608 million. If the toxic cloud moves in, the dollar loss could be staggering.

Dr Barbara Hickey of the UW Oceanography Department says her best guess is that the cloud will not come in to the coast. But she added: "Can you predict the weather? It all comes down to be able to predict the weather."

A NOAA scientist says the cloud is as toxic as clouds that killed sea lions and otters in California.

Dr Vera Trainer says that probably won't happen here, but birds may be at risk: "We saw a number of sea birds feeding on herring in the light of the ship's equipment; and I was wondering as I was watching birds feeding on plankton, 'What is the fate of these birds?' "

Only time will tell.

The good news is that scientists will be tracking the cloud by drogues dispersed on the water and receiving data from satellites. The bad news is, if it is heading for our coast, there's nothing they can do.

The scientists are trying to determine why these plankton, which are common up and down the Pacific Coast, become toxic. One possibility appears to be when ocean currents stir up iron-rich soil.

They are also studying whether fertilizer and untreated sewage might be involved, but the scientist told KOMO 4 News this is only an outside possibility and it appears 90 percent of the causal factors may be related to ocean events and the weather.

One way to disperse the toxic plankton might be a massive release of water down the Columbia River. But that is unlikely because the Columbia is managed to help endangered salmon runs.