GRANITE FALLS, Wash. - Pilchuck River in Snohomish County may run pink or rust-colored Tuesday as researchers test water quality using a non-toxic dye.

Scientists with the Ecology Department plan to release the dye at two locations on the river at dusk Tuesday. They'll track the dye as it moves downstream.

"It'll tell us how long it takes water to go from the top to the bottom," said Nuri Mathieu, one of the scientists working on the project.

The agency says the dye doesn't harm people, plants or fish.

Stretches of Pilchuck River are currently too warm and doesn't have enough oxygen, making it harmful to fish and other aquatic life. The river currently doesn't meet certain clean-water standards. It flows from the Cascade Mountains east of Granite Falls to Snohomish before joining the Snohomish River.

Researchers will collect river water samples over four days and gather data on temperature, dissolved oxygen and nutrients.

The scientists will use the data to figure out where they should plant more trees along the banks, all in an effort to bring more shade and cooler temperatures to the river.

The information will ultimately guide the department and others in their cleanup plans.