On summer weekends the Chesapeake & Ohio Canal National Historical Park is crowded with stroller-pushing families, hikers, cyclists and fishermen. But despite its popularity, the C&O Canal is one of the nation's most deprived national parks.

The canal runs for 184.5 miles along the Potomac River from Georgetown west to Cumberland. It is what remains of George Washington's vision of connecting western land to the east by a series of canals. Today 3 million people a year visit the canal, most never suspecting that they are enjoying one of the most diverse ecosystems and most culturally significant areas in the eastern United States.

But like nearly all our national parks, this special place is in jeopardy. An analysis of the C&O Canal's 2001 finances revealed that the park had only 37 cents for every dollar it needed to operate. As a result, historic lock houses and other park buildings, such as Pennyfield, which once hosted President Grover Cleveland as an overnight guest, are crumbling. Stories about American Indian villages, Civil War military camps and Tobeytown -- a community of former slaves located by the canal -- go largely unknown. Only one person staffs some visitor centers, and if that person has the flu, the visitor center is closed.

To stretch their pennies, park managers have relied on individuals and private groups to provide funding and elbow grease. Volunteers have restored lock houses, maintained trails and removed invasive plants; in 2003 they donated 45,000 hours of service. But depending on volunteers means only marginal survival for the park.

Nationwide, national parks struggle under the weight of an annual operating shortfall of more than $600 million, with the Congressional Research Service reporting a backlog of deferred maintenance projects costing as much as $9.69 billion.

Thankfully, the National Park Centennial Act, introduced in Congress this spring by a bipartisan group of Republicans and Democrats, seeks to increase funding for the maintenance and preservation needs of our national parks through 2016 -- the 100th anniversary of the park system's creation. The legislation provides new funding for the parks, in part through a voluntary check-off on federal income tax returns, which allows taxpayers to donate all or part of any refund to the parks. In a recent nationwide poll, three in five respondents said that they would donate to the parks via a voluntary check-off.

This isn't the first time the C&O Canal has needed our help. The canal ceased operations in 1924. Thirty years later the government wanted to put a highway over it, but Supreme Court Justice William O. Douglas challenged The Post and other supporters of the highway plan to join him on a walk along the length of the canal in 1954, the better to appreciate its historic and natural qualities. By the time Douglas arrived in Washington two weeks later, an outpouring of public support had generated the momentum to save the old waterway. The C&O was designated a national historical park in 1971.

The threat to the park has changed now, but the solution remains remarkably similar: a few steps in the right direction and broad public support.

I am grateful that Reps. Elijah Cummings (D-Md.), Chris Van Hollen (D-Md.) and Frank Wolf (R-Va.) have lent their support to the Centennial Act. As of today, this bill has more than 50 Republican and Democratic co-sponsors in the House and five co-sponsors in the Senate. All of Congress should join these local leaders and the other champions of our national parks in supporting this effort.

As park users, we too must stand up for the C&O Canal, through volunteering or through contacting our congressional representatives to express our desire to protect and restore America's priceless heritage -- as well as our local treasure, the C&O Canal.

-- William L. Withuhn

is a member of the nonprofit National Parks Conservation Association.