Oregon Public Broadcasting

The discovery of E. coli bacteria in a Portland reservoir has forced city officials to dump millions of gallons of water. But they say there’s no health risk.

A routine test of Mount Tabor’s smallest open reservoir came back positive for E. coli on Monday.

It’s the first such discovery since Thanksgiving, when the city found E. coli in a Washington Park reservoir.

Thousands of residents were asked to boil their water. There’s no boil-water order this time, and there have been no health problems traced to the E. coli.

Water bureau administrator David Shaff says the difference this time is that additional tests didn’t confirm the bacteria’s presence.

David Shaff: “We re-sampled, and all of our regular samples Monday, and all of our regular samples Tuesday, all of our additional samples Tuesday came back negative except for just that one for Reservoir Number One.”

Shaff says one-time E. coli discoveries have happened more than a dozen times over the years, with last Thanksgiving as the only instance where E. coli was confirmed on another test.

In a new step since the November discovery, the water bureau is dumping all nine million gallons of water from the affected reservoir -- after just the one positive test. 

Water officials drew criticism last year for not acting quickly enough to confront the E. coli problem.