GRANITE FALLS — Swimmers, floaters or neighbors may notice tendrils of pink swirling in the current of the Pilchuck River this week, but it’s no cause for concern.

Researchers planned to release a fluorescent pink dye called Rhodamine into the river Tuesday evening at two locations. One is where the river passes under Menzel Lake Road and the other is at 64th Street. It’s part of a four-day-long research project to test water quality in the Pilchuck.

Over the next couple of days, teams of scientists from the state Department of Ecology are scheduled to take samples at different points downstream to see how the Rhodamine is distributed and what condition the water molecules are in. They have equipment that can detect the presence of the dye long after the color fades from human perception.

The Rhodamine essentially marks water molecules so the researchers can learn from tests how the river behaves. They’ll use the data to build computer models of the river and eventually develop a clean-up plan for the Pilchuck. They’re testing how quickly and where the water molecules are carried by the current. They also are gathering information about temperature, oxygen content, nutrient levels and acidity.

Stretches of the Pilchuck River, which runs from the North Cascade Range through Granite Falls and toward Snohomish, do not meet state standards for water quality. The temperature is too high and the oxygen content is too low, according to the Department of Ecology. State teams have been researching the river extensively since 2012 and this week’s project builds on those studies, water quality specialist Ralph Svrjcek said.

High temperatures and low oxygen content create poor conditions for fish and other animals in and around the river.

“We just want to understand that better and turn it into a healthy place for returning salmon and trout who live there throughout the year,” Svrjcek said.

This week’s study also involves putting in multiple groundwater monitoring wells to examine how the quality of groundwater affects water quality in the river.

The results of this week’s research are expected to be released next year, in time to be incorporated into a clean-up plan. The Department of Ecology plans to form an advisory group next spring or summer to draft the plan. It should include representatives from local governments, conservation districts and tribes, Svrjcek said.

Clean-up plans typically include proposals such as adding trees and plants alongside rivers and removing some aquatic plants from within the rivers. At night, plants consume oxygen in the water, which means that too much plant life in the river can deplete the oxygen supply for fish.

Planting more trees and bushes alongside the river stabilizes the bank so less sediment gets into the water and shades stretches of the river where the water is heating up.

“One of the very basic things is that we want to get trees planted where there are none,” Svrjcek said. “Every place that we plant a tree, we can keep the sun off the water and keep it in its more typically cool state.”

People who live along the river also can help improve water quality by planting trees along the bank and not throwing any clippings or yard waste into the river.

The computer model should be able to tell researchers where the problem areas are along the river so they can focus their clean-up efforts there.

“We need that last bit of data to make sure the model is running properly,” Svrjcek said. “We really want to get the big picture right now and weigh that against what the fish need and what we can do to help them.”

Kari Bray: 425-339-3439; kbray@heraldnet.com.