Runoff turns Elliott Bay into murky stew

To measure just how murky Elliott Bay is, Chris Wilke lowered a black and white disc over the side of the Puget Soundkeeper Alliance's small boat. A scant 8 inches below the surface, and the disc was lost from view — swallowed up in water the color of milky coffee.

On an ordinary winter day, the disc is visible from 3 feet underwater.

"I've never seen it this muddy before," said Wilke, who has worked with the alliance for eight years.

Several days of heavy rainfall in the Green/Duwamish River watershed, combined with high water releases from Howard Hanson Dam 65 miles upstream from the bay are responsible for the brown layer spread over much of the bay.

The grunge extends well past the Magnolia-area marina where the Soundkeeper Alliance moors its boat.

"It just goes to show you where the stormwater goes," Wilke said as the boat pulled away from the dock Wednesday for a weekly patrol across the bay and up the Duwamish.

Rain-driven erosion and landslides swept sediment into the river several days in a row. While precipitation in the urban areas wasn't extreme, some upstream areas got more than 7 inches in 72 hours. Much of the rain fell on snow, adding to the gush, said National Weather Service meteorologist Dennis D'Amico. "They got hammered in the mountains."

Heavy flows from the Howard Hanson reservoir, which must be lowered to make room for the next round of rain, have kept the pot stirred by kicking up mud from the river bottom, said Debra Williston, of King County's Department of Natural Resources and Parks.

A county water-monitoring station at the Seattle Aquarium logged the rising sediment levels, denoted as turbidity, beginning late Monday and extending through Wednesday. Though the rain has stopped, the National Weather Service says the river is expected to remain high over the next few days — and more rain could fall later this week.

The aquarium pulls and filters water directly from the bay for its exhibits, some of which are less crystalline than usual as a result of the murk, said spokesman Tim Kuniholm. He takes in the waterfront view every workday, and it's startling.

"It looks like the Mississippi," he said. "It's brown and green and pea soupy."

It's not uncommon for silt-laden water to color the bay after major rainstorms, but the Duwamish hasn't been this high in two years, said Doug Williams, a spokesman for King County.

The lighter freshwater "floats" on the surface of the saltwater. The murk can include a stew of contaminants, from oil residue scoured off city streets to effluent from leaking septic systems.

Not that many would chose to swim this time of year, but the Washington Department of Ecology (DOE) cautions against it. Several commercial shellfish beds also were closed temporarily because of concerns over contaminated runoff in coastal areas.

"It's really unusual," said Jessica Archer, of DOE's swimming-beach program. "All of the bays are brown right now."

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com

Information in a photo with this story, originally published Jan. 19, 2011, was corrected Jan. 20, 2011. A previous version of the caption incorrectly stated a person's name. The correct name is Chris Wilke, shown in the second photo.