Since parks were created in part for enjoyment by people, present and future generations, the element of human sound is necessarily present. For example, roads, trails, facilities, visitors, and park operations represent sources of sound. The irony, which represents the crux of many soundscape issues in national parks, is that people who wish to enjoy the natural values are by this act directly or indirectly affecting the quality of the resource itself.
Some who enjoy national parks using certain modes of access at the same time create noise that impacts the experience of other visitors. While one is viewing the park via an air tour, an auto, a snowmobile, personal water craft, motorcycle, or a bus, noise is created for other people who have an expectation of quiet, solitude, or appreciation of natural sounds. Adding to the difficulty, people who use these modes of access are not often aware of the impact on other people and on wildlife. Perhaps the most extreme example of this is in the use of air tours to visit parks.
Other sources of noise are ambient, originating beyond the park boundaries, and beyond the regulatory authority of National Park Service. These include aircraft overflights of a commercial or military nature, at higher elevations, depending on the proximity of the park to a commercial airport or military installation. Distant highway traffic and motorized vehicles using adjacent public lands are other common sources of sound affecting a park.
The soundscape of an area is not just limited to the terrestrial environment. Underwater sounds can also be disruptive to marine species. At Glacier Bay National Park, analysis of underwater noise generated by fishing and recreational vessels indicated that these sounds disrupted the behavior of marine mammals, and the park is monitoring underwater sounds.