The water in Milliken Creek ran red — the color of tomato soup, said one observer — as it passed through Silverado Resort Wednesday afternoon and evening.
Bob Creamer, who lives at Silverado, watched the crimson flow from his desk and wondered if someone had thrown dye into the stream.
Joy Eldredge, the city of Napa’s water general manager, provided an explanation Thursday for the crimson flow.
According to Eldredge, the water was colored by iron in the soil and rock in Milliken Canyon as the city prepared to start up the water treatment plant above Silverado Resort in northeast Napa.
The iron-rich water never entered the city’s water distribution system since the Milliken plant is still not operating, Eldredge said.
City employees have taken samples of the red water for lab analysis and will consult with biologists as to its impact on stream life, she said. If the red flow continued for days, it could hurt small fish, she said.
As of Thursday morning, the color of Milliken Creek, which flows into the Napa River, had gone from red to a muddy brown, Creamer reported.
As part of starting up Milliken treatment plant for a late-summer run, Eldredge said the water department released water from Milliken Dam off Atlas Peak Road on Wednesday and ran it overland for about 800 feet before recapturing it for the pipe that leads to the plant.
By the time the water got to the pipe, it had made contact with collapsed banks rich in iron that colored it red, she said.
If the plant had been in operation and had encountered such iron-rich water, it would have automatically shut down, Eldredge said.
The water in Milliken Reservoir is some of the purest in the city’s system, but it tends to be high in minerals, including iron, she said.
The city gets most of its water from Lake Hennessey and the State Water Project.