RELATED: This One Type of Mask Won’t Protect You From the Delta Variant, Expert Says. On Aug. 16, the National Park Service (NPS) announced a mask mandate for all visitors, employees, and contractors, whether vaccinated or not. Masks will be required inside all NPS buildings and even in crowded outdoor spaces within the parks, effective immediately. “This requirement will be in effect until further notice and applies to all NPS buildings and public transportation systems,” the announcement reads. “It also applies to outdoors spaces where physical distancing cannot be maintained, such as narrow or busy trails and overlooks.” The NPS says this mask mandate is in place in all national park areas, no matter community transmission levels. Under the CDC’s latest guidance, only areas with substantial or high transmission are encouraged to enforce indoor mask requirements. But during an Aug. 12 White House COVID briefing, CDC Director Rochelle Walensky, MD, said that more than 90 percent of U.S. counties now fall within these levels. “Visitors to national parks are coming from locations across the country, if not across the world. 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 Deputy Director Shawn Benge said in a statement.ae0fcc31ae342fd3a1346ebb1f342fcb RELATED: For more up-to-date information, sign up for our daily newsletter. National parks have seen a significant rise in visitors during the 2021 travel season. In July, Stephanie Roulett, a spokesperson for the U.S. National Park Service, told CNBC that “many campgrounds and lodging in and around popular destination national parks—places like Yosemite, Yellowstone, Zion, Glacier, and Acadia—are already fully booked or nearly fully booked through Labor Day.” Officials say this mask mandate will help protect all guests, as parks are allowing unvaccinated individuals to visit. “Being vaccinated is the most effective way to protect yourself and your loved ones from the dangers of the coronavirus. 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,” Maria Said, MD, an epidemiologist in the NPS Office of Public Health and a member of the U.S. Public Health Service Commissioned Corps, said in a statement. Alongside masks, other public health measures may be in place at national parks across the country, including capacity limits, entrance reservations, one-way trails, and temporary closures. The NPS recommends that you check individual park websites for specific details before planning a trip. RELATED: Virus Experts Have Stopped Going to These 4 Places as Delta Surges.