One-and-a-half-weeks in, the government shutdown is already taking a toll on some of country's most iconic national parks. The parks have remained largely open to the public despite the fact that most of the rangers and other support staff who maintain them are among the hundreds of thousands of government workers now on furlough, and the unsupervised access has led to a buildup of trash and a break-down in visitor behavior, The Associated Press reported Tuesday.

During many previous shutdowns, the parks had closed their gates, but the Trump administration chose to keep them open.

"We're afraid that we're going to start seeing significant damage to the natural resources in parks and potentially to historic and other cultural artifacts," Senior Budget Director of the nonprofit National Parks Conservation Association John Garder told The Associated Press. "We're concerned there'll be impacts to visitors' safety. It's really a nightmare scenario," Garder said.

The shutdown plan does give park superintendents the power to close down certain sites or areas if garbage or other problems pose too great a danger to humans or wildlife, National Park Service spokesman Jeremy Barnum told The Associated Press by email. And some parks have already decided to do just that.

Here is a breakdown of how the shutdown has already impacted some beloved parks.

1. Yosemite

Yosemite National Park had to close two campgrounds and the popular Mariposa Grove of redwoods because of a buildup of human waste along the side of road, The Los Angeles Times reported Monday. With restrooms shuttered, visitors had been relieving themselves off of Wawona Road, which is also California Highway 41, posing a health risk for other visitors.

"It's a free-for-all," 24-year-old Yosemite Valley resident Dakota Snider told The Associated Press of conditions in the park. "It's so heartbreaking. There is more trash and human waste and disregard for the rules than I've seen in my four years living here."

2. Joshua Tree

Joshua Tree National Park in the Mojave and Colorado deserts of Southern California has been forced to close all campgrounds starting Wednesday, The San Bernardino Sun reported. Conditions at the park have deteriorated as pit toilets overflow, visitors let their dogs off their leashes and drive off road, and people set up camp in protected areas or sites reserved by others.

The situation has been improved somewhat by volunteers from Friends of Joshua Tree and local businesses, who have raised $5,000 to take out trash and clean toilets. But the work is getting to be too much for the volunteers, Cliffhanger Guides co-owner Sabra Purdy told The Sun.

"It is not sustainable to have volunteers keep doing this," Purdy, who took out three pick-up-truck loads of trash from a campground Monday, said. "We can't afford to wipe all the bottoms who visit Joshua Tree."

3. Sequoia and Kings Canyon

Sequoia and Kings Canyon National Parks, twin parks in California's Sierra Nevada mountains, had to close a variety of sites as of 6 p.m. on Monday because of a trash overflow, USA Today reported Tuesday.

"The parks are being forced to take this action for health and safety concerns," the parks' public affairs officer Sintia Kawasaki-Yee said in a press release reported by USA Today. "Trash receptacles are overflowing, resulting in litter dispersal throughout the area and a threat to wildlife."

4. Rocky Mountain

In Colorado's Rocky Mountain National Park, staff began closing toilets and locking trash bins because of unspecified health and safety concerns, CBS4 Denver reported Tuesday.

"Park staff are beginning to close restroom facilities and trash receptacles at many park locations due to human waste issues, wildlife concerns and overall public health," the park said in a statement.

The park has also had to close down some roads due to snowfall because it does not have the staff to sand or plow them.

5. Yellowstone

Access to Yellowstone National Park has also been threatened by snowfall. Normally, during the winter, vehicle access is blocked off and visitors access the park via snowmobile tours over pre-groomed trails. With the park service unable to maintain these trails, private companies are splitting the cost of keeping them clear, as well as replacing toilet paper and emptying trash, so they can continue to run tours. See Yellowstone Alpen Guides General Manager Travis Watt told The Associated Press that the tour companies could continue to do this throughout the winter if they have to.

"It's definitely not our preference—the park service does a good job doing their thing and we hate to see them out of work," Watt told The Associated Press. "But it's something we can handle."