The waters of Whidbey Island will run red Monday with the fluorescent hue of rhodamine, a non-toxic dye being used by the state to survey wastewater movement and its impact on local shellfish.

The Washington Department of Health is evaluating the movement of wastewater near the Oak Harbor Clean Water Facility and its impacts on shellfish growing areas, primarily those near the Saratoga Passage and Penn Cove.

The evaluation was to start Friday and run through Wednesday. The dye, which will be used Monday morning, could be visible for roughly a day in waters surrounding Oak Harbor.

The Clean Water Facility, which finished construction in November 2019, treats 100% of Oak Harbor’s sewage and wastewater. The facility is one of four wastewater treatment plants on Whidbey Island, With a price of $150 million, it’s the most expensive and complex.

The survey, which had been scheduled for 2019 after the facility was finished, was delayed until now because of technological issues and, later, the pandemic. It will be conducted by the Department of Health, which oversees commercially harvested shellfish in Washington, in partnership with several state and federal agencies as well as the city of Oak Harbor, Island County and local shellfish growers.