Despite the pronouncement, however, damage to the Environmental Protection Agency's standing in the region appeared far from recovered, with state and tribal officials describing a lackluster initial response to the Aug. 5 incident that unleashed 3 million gallons of mustard-colored mine waste into the river near Durango.
Gov. John Hickenlooper, a Democrat, said he shared his constituents' anger at the spill and the EPA's subsequent response to it. The Navajo Nation, situated downstream in New Mexico, said they planned to take legal action against the federal government. And the attorneys general of Utah, Colorado and New Mexico were on a fact-finding mission at the spill site before determining their own legal paths forward.
Even in Washington, Republicans were taking aim at the Obama administration for its response to the spill.
"This EPA spill is very serious, as is the EPA's slow response," House Speaker John Boehner wrote in a statement. "The Obama administration must do everything in its power to protect the lives and livelihoods of the people in the affected states."
"Now that his EPA has accepted full responsibility, I expect President Obama to demand full accountability for what happened here," Boehner added.
The White House wouldn't say Wednesday whether Obama, currently vacationing on Martha's Vineyard, had been recently briefed on the spill.
Instead, EPA Administrator Gina McCarthy has taken responsibility for managing the aftermath and restoring the EPA's reputation. She said Tuesday that she and her aides were keeping the White House abreast of the situation.
A popular figure within the White House, McCarthy has become one of the key figures of Obama's climate agenda as he looks to solidify his environmental legacy.
Because congressional action on climate change has stalled, much of the administration's moves toward curbing climate change have come through new EPA regulations, including a major new rule announced last week to cut carbon emissions from power plants by 32%.
McCarthy figured heavily into the announcement, which was made from the White House two days before the spill.
She traveled to Colorado on Wednesday to assess the plume of contaminant, and said her agency was committed to both an internal and an independent investigation of the incident.
"EPA's mission is to protect public health and the environment," she said. "We couldn't be more sorry."
On Wednesday, Republican lawmakers demanded the agency's inspector general launch an independent review of the incident, citing the agency's own demands of "nothing less than complete transparency" surrounding the 2010 BP oil spill in the Gulf of Mexico.
"That standard also applies to the ongoing environmental disaster that has now touched several western states," the lawmakers wrote.
McCarthy said on Wednesday there would be an independent review on the spill, though she didn't specify who would conduct it.
Saying she was committed to learning lessons both from the incident itself and the EPA's response to it, she emphasized that agency investigators -- normally tasked with probing spills from private sector firms -- wouldn't be biased in their own assessments.
"We will hold ourselves to a higher standard than anyone else," she said.