The head of the Environmental Protection Agency says samples of waters that flow through three Western states, contaminated by waste from an abandoned Colorado mine last week, are showing improvement. Experts say the heavy metals and other materials are still there, though, in the riverbeds.

Speaking to reporters today from Durango, Colo., EPA Administrator Gina McCarthy promised more details later but did provide what she called "very good news."

"We have water quality data from Aug. 7, 8 and 9 from La Plata County and it shows that the levels have returned to pre-event conditions," McCarthy said.

It was not quite an "all clear," though.

The Associated Press reports that the riverbed remains tainted:

" 'There will be a source of these contaminants in the rivers for a long time,' said hydrologist Tom Myers, who runs a Nevada-based consulting business. 'Every time there's a high flow, it will stir it up and it will be moving those contaminants downstream.' "

McCarthy said EPA will work "with our counties and our local communities so that they can have a chance to review this data thoroughly and they can have a full opportunity to talk through what this means in terms of decisions they're going to make moving forward."

"The very good news is that the data so far is showing that water quality does restore itself to its prior conditions," McCarthy said.

It's been a week since a toxic flood of heavy metals, arsenic and other materials from the Gold King Mine spilled into the waterway, turning it a vibrant mustard color.

McCarthy announced the EPA would be conducting an internal investigation as to what caused the Aug. 5 spill. The EPA chief also said her agency will seek an independent review of what happened.

The Denver Post reports:

"While in the region, McCarthy is not planning a trip to the Gold King Mine, nor is she holding a public meeting. The incident, she said, was a 'heart-breaking situation.' "

McCarthy reiterated points she made ahead of her trip to Colorado, saying, "No agency could be more upset about the incident happening" and that the EPA is taking full responsibility.

As we've reported, the spill was triggered last week when an EPA cleanup team breached a dam at an abandoned Colorado mine.

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