(CNN) — If you want to visit one of America’s national parks, there’s an essential item you must bring: face masks.

Visitors, employees and contractors are now required to wear a mask inside all NPS buildings and even in crowded outdoor spots. This applies regardless of your vaccination status or transmission levels within the community.

The NPS said it is following the latest science and guidance from the Centers for Disease Control and Prevention.

“Visitors to national parks are coming from locations across the country, if not across the world,” said NPS Deputy Director Shawn Benge in a news release.

“Because of this, and recognizing that the majority of the United States is currently in substantial or high transmission categories, we are implementing a service-wide mask requirement to ensure our staff and visitors’ safety.”

NPS: Get vaccinated — and enjoy

This requirement will be in effect until further notice, the NPS said. It applies “to all NPS buildings and public transportation systems. It also applies to outdoors spaces where physical distancing cannot be maintained, such as narrow or busy trails and overlooks.”

“Being vaccinated is the most effective way to protect yourself and your loved ones from the dangers of the coronavirus,” said Capt. Maria Said, an epidemiologist in the NPS Office of Public Health and a member of the US Public Health Service Commissioned Corps.

“Masking in addition to being vaccinated will help prevent the spread of new variants and protect those who are more at risk of severe disease. This simple act of kindness allows us to be safe while we continue to enjoy the benefits of our national parks.”

Big park attendance this summer

Earlier this summer, Arches National Park was having to turn away visitors eager to get out into wilderness areas.

Earlier this summer, Arches National Park was having to turn away visitors eager to get out into wilderness areas.

Leslie Perrot/CNN

When the 2021 summer travel season first unfolded and the Delta variant had not yet become widespread, Americans flocked to parks in huge numbers.

Arches National Park in Utah was one of a number of headliner parks that saw significant overcrowding. The influx of visitors forced the park to temporarily shut its gates almost daily.

Potential visitors to big-name parks such as Yellowstone and Yosemite were encouraged to try out less popular parks to avoid crowds, long wait times and possibly being turned away.

The CDC says that outdoor activities remain the safer choice, especially if you continue to stay 6 feet apart from people you don’t live with.

Activities such as hiking in uncrowded areas and roasting marshmallows by a fire are still considered less risky ways to spend your leisure time.

Top image: Visitors walk to the Tunnel View lookout at Yosemite National Park, California, in July 2020. (Apu Gomes/AFP via Getty Images)