Portland water officials said they need to discard 38 million gallons of water after a 19-year-old man urinated in the reservoir on Wednesday at 1 a.m. PT.
Two other men, aged 18 and 19, then tried to jump over the fence and one of them entered the reservoir.
Water samples from the reservoir were taken for testing, and results will be available on Thursday.
In 2011, it cost the water bureau $32,700 rate-payer dollars to discard 8 million gallons of water from the same reservoir after a 22-year-old man admitted to urinating in it.
Update — May 1, 10:55 a.m. ET: Turns out the reservoir may not get flushed after all, according to NBC News. The Portland Water Bureau says the water will be kept as an experiment to monitor a reservoir's water quality over time.
Tasneem Nashrulla is a reporter for BuzzFeed News and is based in New York.