The National Park Service turns 100 this year. As the agency celebrates its centennial, it finds itself in a seemingly paradoxical circumstance: widely admired but increasingly uneasy about its ability to carry out its mission. The agency and the iconic parks it manages need our help.

Poll after poll rates the agency among the very best in government. In a recent national Gallup poll, for example, respondents rated “national parks and open space” in second place among a list of 19 federal government functions. Sentiment toward the national parks and the National Park Service may have been most powerfully expressed by the widespread public outrage over closure of the national parks during the most recent government shutdown. The more than 300 million annual visits to the national parks is another testament of their value to Americans.

It’s paradoxical that an agency with such a public spirited mission and broad and longstanding public support would be in the midst of a crisis in morale during its centennial. In a 2015 survey of satisfaction and related issues among federal employees, the National Park Service received an index score of 53.1 (out of 100), placing it 259th out of 320 agencies; the score has fallen nearly 10 points over the last decade. Employees believe deeply in the mission of the Park Service and have prepared themselves to carry out this work, but the agency lacks the resources to fully meet its mission and places too high a burden on its rangers and other staff.

The permanent workforce of the National Park Service has dropped below 20,000, fewer than the number of employees at Disneyland, and its annual budget accounts for less than one-tenth of 1 percent of the federal budget and is falling substantially in real dollars.

Consequently, the national parks have accumulated more than $12 billion in deferred maintenance. Add in the increasingly urgent challenges facing the national parks — climate change that threatens the integrity of the parks, for instance — and it’s no wonder the agency is worried about living up to its mission.

What can be done? Of course Congress and the federal government simply must make investing in the national parks — which writer and conservationist Wallace Stegner famously called “America’s best idea” — a priority.

But ordinary citizens can also help by celebrating the centennial with a commitment to service: by volunteering at a visitor center, monitoring sea turtle nests, rebuilding a storm-damaged trail, helping organize historical archives, donating to a park friends group and a myriad of other actions. Perhaps above all, we can help by becoming informed national parks voters.

In partnership with public, private and nonprofit groups, those of us who love the parks must do what we can to help the National Park Service accomplish the important work for which it was created 100 years ago, and promote the self-esteem of its dedicated employees in the process.

In this way, the national parks are more certain to be protected in what will be a challenging second century.

Robert Manning is a professor of environmental and natural resources at the University of Vermont and the co-editor of the new book, “A Thinking Person’s Guide to America’s National Parks.”