Some of America's iconic national parks are in danger of being overwhelmed by rubbish and could suffer significant damage due to the partial shutdown of the US government, conservationists have warned.
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Donald Trump said he had "no choice" but to continue the shutdown, blaming Democrats as litter and human waste piled up at tourist areas around the country.
Dakota Snider, 24, who works in Yosemite Valley, said: "It's so heartbreaking. There is more trash and human waste and disregard for the rules than I've seen. It's a free-for-all."
The US government has been partially shut down for 11 days due to a standoff between Mr Trump and Democrats in Congress, who are refusing to authorise $5.7 billion to fund a large part of the president's proposed wall on the Mexico border.
Hundreds of thousands of public employees have been sent home, including rangers and other park staff.
Unlike in previous government shutdowns national parks and campgrounds have remained open without staffing.
John Garder, of the National Parks Conservation Association, said: "It's really a nightmare scenario. We're concerned there'll be impacts to visitors' safety."
In California the Sequoia national park, home to ancient sequoia trees, was closed due to overflowing rubbish bins.
At Joshua Tree national park rows were reported between campers with no rangers to step in, and damage was being caused by visitors illegally going off road in vehicles.
Litter also piled up on the National Mall in Washington.
Mr Trump stayed in the capital over the new year, canceling a trip to Florida. White House officials indicated the president believes he has public opinion on his side, and that Democrats will be blamed for the shutdown.
Democrats take control of the House of Representatives on Thursday and said they would introduce a spending bill to fund the government, but it contained no money for a border wall.
Mr Trump wrote on Twitter: "The Democrats, much as I suspected, have allocated no money for a new Wall. So imaginative!
"I'm in Washington, I'm ready, willing and able. I'm in the White House, I'm ready to go. They can come over right now, they could've come over anytime."
He added: "The wall is not old-fashioned. The wall is one-hundred percent foolproof. No, we are not giving up. We have to have border security and the wall is a big part of border security. The biggest part. The Tech 'stuff' is just, by comparison, meaningless bells and whistles."