In this June 18, 2021, file photo, U.S. Sen. Angus King, I-Maine, speaks at Acadia National Park in Winter Harbor, Maine. Credit: Robert F. Bukaty / AP

BAR HARBOR, Maine— Senators from Maine and Montana want the Biden administration to clarify the impact of more people visiting the country’s national parks.

Independent Sen. Angus King of Maine and Republican Sen. Steve Daines of Montana said last week they want to know the impact of increased attendance on the parks, visitors and surrounding communities. They’ve called on National Park Service Director Charles Sams for a congressional briefing about the subject.

The senators said there have been “historic numbers of National Park visitors,” including at Yellowstone National Park and Acadia National Park. Yellowstone saw annual visits increase from about 3.6 million in 2010 to nearly 4.9 million last year, they said. The senators said Acadia’s attendance grew from about 2.5 million to about 4.1 million in that time.

The senators wrote that the park system “is one of our nation’s greatest treasures, and as such we must be vigilant in ensuring that they continue to be available for the benefit and enjoyment of the people of this and future generations.”

The National Park Service administers more than 400 national parks across the country. It compiled a list of the most visited parks last year, with the Blue Ridge Parkway spanning the southern and central Appalachians topping the list with 15.9 million visitors. Yellowstone ranked 12th and Acadia was 16th.

Like Acadia, the Cape Cod National Seashore also had 4 million visitors, ranking 17th.