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More than 200 million gallons of sewage spilled into the Potomac River this month, driving bacteria near the break to extreme levels. Washington Aqueduct officials said the incident is an ecological disaster but is not affecting drinking water supplied to D.C., Fairfax County and Arlington County.

The aqueduct draws its water primarily from the Great Falls Pumping Station, several miles upstream from the spill site just south of the American Legion Bridge.

“Our water quality is excellent,” aqueduct General Manager Rudy Chow said. “We meet and exceed all EPA environmental requirements under the Safe Drinking Water Act.”

Officials increased water-quality testing from five days a week to seven during the incident.

Conditions are far worse at the Little Falls Pumping Station downstream from the spill. Samples there have shown very high concentrations of bacteria, fecal coliform and E. coli, according to Chow. Although those levels have declined somewhat since D.C. Water stopped the overflow a week ago, they remain thousands of times higher than the normal average.

Little Falls has been offline since before the break and is not expected to be needed soon. The station is generally used during the summer, when weaker river flow into Great Falls coincides with higher demand.

Chow said Little Falls will remain closed until water quality returns to normal.

“We’re not taking any water from there at all,” he said. “Our water is all upstream from here, and the concentration and water quality is normal as always.”

Officials expect contamination downstream to continue declining if no additional sewage enters the river and its flow keeps diluting the spill as it moves south.

The Army Corps of Engineers also said the spill is not affecting water treatment at the Dalecarlia plant in Northwest D.C.