GLACIER NATIONAL PARK - Future visitor restrictions on the Going-to-the-Sun Road corridor? Impacts from oil and gas development east of the park? Aquatic invasive species as Glacier National Park's biggest threat?

These are some of the topics on Glacier Superintendent Chas Cartwright's mind as he winds down to retirement at the end of the year after 25 years with the National Park Service.

Since Cartwright came to Glacier in spring 2008 from a superintendent's position in Shenandoah National Park, he says he's gotten a good handle on working with community and business leaders around the park, and "that's the downside" of retiring.

But he's also a bit tired of the stress and having to contend with bureaucracy.

"It's just time to move on," he said.

Asked about the pressures that result from the park's recent busy summer seasons, including record high visitation of 2.2 million people in 2010, Cartwright concedes that the park is "near capacity," particularly in the Sun Road corridor.

"Some people are staying away because it's so congested," Cartwright said, referring mostly to local visitors who prefer going to the park in the spring and fall shoulder seasons. "We're way busy in the summer, and I don't imagine we could accommodate many more people."

He referred to the severe parking congestion at Avalanche Campground and Logan Pass as falling short of success in managing the corridor.

"I do envision tighter management of that corridor," he said.

Cartwright noted that a common response to increase capacity in a national park is to simply propose larger parking areas, but that doesn't account for the totality of resource impacts.

"Use on the Highline (Trail) has gone through the roof," he said.

There are other ways to address the issue, such as issuing a limited number of parking permits for certain areas or relying more on mass transportation.

The park has had a shuttle system for several years, but Cartwright suggested the system is not sustainable the way it is currently being operated. The free shuttles are supported by $7.50 from park entry fees for a total budget of about $800,000 annually, which is not enough to keep it going, he said.

The objective of the system was to mitigate impacts on visitors while a long-term reconstruction project was under way on Sun Road, primarily by encouraging visitors to park their cars at Apgar or St. Mary. But surprisingly, Cartwright said, the system has managed to reduce vehicle traffic on Sun Road by less than 1 percent.

"The real complaint is there isn't enough of it," he said of the shuttle service.

Cartwright said it's likely that future park leaders will need to consider charging people who use the service, or find other revenue sources to support it. The system will need more money as the larger buses and smaller Sprint shuttles age, requiring more maintenance or replacement.

On the park's eastern end, Cartwright said he is concerned about potential impacts from oil and gas development on the Blackfeet Reservation.

"That's a tough issue, because it's a decision of the Blackfeet Nation," he said. The park can only give advisory input, even though the impacts could be huge.

So far, there are 18 exploratory wells on a swath of land adjacent to the park, but another 18 have been approved and about a dozen more could be.

"If you've seen oil and gas that's been done well, it's fine," he said, but he noted that only happens with the very best planning, technology and development.

The park's biggest concern is how development has been reviewed one well at a time, when the preference would be a review that accounts for cumulative impacts from multiple wells.

And cumulative impacts can be immense, he said, citing Theodore Roosevelt National Park in North Dakota, which is now surrounded by thousands of oil and gas wells, which has a huge effect on the visitor experience.

"My view is that it's not the same, and I don't want that to happen with Glacier National Park," he said.

Cartwright describes relationships with the Blackfeet Nation as being "challenging."

He referred to a tribal resolution from the summer of 2011 calling for the tribe to manage not just the east side of the park but the entire park.

Taking Glacier out of the hands of the National Park Service and putting it under any other management entity "is not a good idea," he said.

Cartwright didn't hesitate in saying that "aquatic invasive species are the biggest threat the park has right now."

Zebra and quagga mussels, in particular, have been proliferating across the West, causing immense economic and environmental damage. Transported on watercraft across state lines, the prolifically reproducing mussels have wreaked havoc on water systems, dams and other infrastructure around water.

Lake Mead in Nevada has been "totally contaminated," Cartwright said, and he thinks all efforts should be made to prevent their introduction in Montana waters.

As chairman of the Flathead Basin Commission for nearly two years, Cartwright said it has been a priority issue, but he is frustrated that the public doesn't seem to grasp the extent of the threat.

"We can keep these things out," he said. "But the way we're acting is that it's inevitable they will get here."

Glacier has established an inspection program and the state has worked with partners for inspections to protect the Flathead Basin. An even more vigilant prevention program would be worth the effort, he said.

Cartwright said an ongoing concern is protecting lakes on the park's west side from invasion by non-native lake trout. Most of the west-side lakes have already been invaded, but there are cases where concrete fish barriers and netting to remove lake trout are justified to protect native bull trout and cutthroat trout, he said.

"Our take on it right now is that it's worth the effort," he said. "I don't think it's a lost cause."

In addition to his 25-year career with the National Park Service, Cartwright worked for 15 years with the Bureau of Land Management and the U.S. Forest Service.

"It has been an honor to be involved with public land management and public service the last 40 years," he said. "I've enjoyed my career and protecting many of the nation's special places."

Cartwright and his wife, Lynda, plan to stay in the Flathead Valley, exploring and enjoying outdoor recreation. Cartwright estimates he's been on most park trails, and has found that he likes more remote areas in the North Fork or Two Medicine the best.