During the 1950s and 1960s, momentum was building among environmental groups and canyon lovers to protect the Colorado River within the canyon. Though Congress approved the construction of Glen Canyon Dam in 1956, Lyndon B. Johnson created Marble Canyon National Monument in 1969, preventing two other proposed dams in Marble Canyon.

The effects of Glen Canyon Dam remain under debate. On the one hand, a tamed river with predictable flows from the timed releases from the dam makes commercial river running possible. On the other hand, native warm-water fish have become endangered and extirpated, and aggressive nonnative plants, such as tamarisk, have overtaken beaches.

The beaches themselves are in danger: The river continues to erode the canyon’s sandy beaches without the periodic flooding needed to replenish them. An environmental impact statement, completed in 1995 after a lengthy scoping period involving several public hearings from Los Angeles to Washington, D.C., concluded that controlled flooding might benefit the canyon. The first controlled flood was staged in 1996, and several have followed.

Controlled flooding is one of the latest attempts to manage or correct species distribution in Grand Canyon. During the early 1900s, hundreds of mountain lions and wolves were killed in order to “protect” deer herds in the Grand Canyon game reserve. This contributed to a tragic overpopulation of mule deer, with a huge die-off from overgrazing, weakening, and disease.

Miners introduced burros to the canyon in the late 1800s, and by the mid-1900s, a feral burro population was impacting desert bighorn sheep. The Park Service’s plan for control included shooting burros from small planes. The Humane Society intervened, leading to federal protection for burros and the ambitious plan to remove burros from the canyon via helicopter. By 1981, nearly 600 burros had been airlifted from the canyon’s depths.

Dam building and other issues spurred discussions between Indian tribes, federal land managers, and environmental groups over how best to protect the canyon’s resources. These discussions resulted in the Grand Canyon National Park Enlargement Act of 1975, which doubled the park’s size to 1.2 million acres and established its present boundaries.

Yet despite physical boundaries, national parks and wilderness areas have little control over airspace or underground resources. The Enlargement Act of 1975 recognized the importance of natural quiet, but the number of tourist flights over Grand Canyon continued to increase after the construction of the airport in Tusayan in 1967. In 1987, Arizona senator John McCain and others won the fight to establish a no-fly zone over the central canyon, setting a precedent for other national parks.

However, nearly 100,000 air tours continue to buzz the east and west two-thirds of the canyon every year. On the river, the use of motorized boats continues to be debated between those who believe the inner canyon’s wilderness should include natural quiet, and those who say limiting tours to non-motorized boats would impact business and limit visitors’ ability to access the inner canyon.

For most visitors, air quality is perhaps the most noticeable environmental concern at the park, especially during the summer, when prevailing winds blow haze northeast from the Los Angeles basin, limiting canyon views. On a clear day, it’s possible to see 200 miles or farther. On some days, haze from a number of sources cuts visibility to less than half that distance.

Grand Canyon Trust, formed in 1985 to lobby Congress about overflights, began negotiating with the Navajo Generating Station regarding the use of scrubbers to reduce sulfur dioxide emissions. Studies conducted by the Park Service showed that the power plant was responsible for as much as 70 percent of the canyon’s visible air pollution. In 1991, the plant agreed to reduce emissions by 90 percent.

Another contributor to haze, the Mohave generating station near Laughlin, Nevada, closed in 2005 due to noncompliance with pollution controls. Over the years, the Trust’s focus has expanded to include sustainable grazing, groundwater protection, species diversity, forest health, and other issues in the Grand Canyon region.

Another very noticeable issue is traffic on the canyon’s busy South Rim. It seemed like a solution was near in 1999, with plans for a light-rail system to cut vehicle traffic by 80 percent. Opposed by private tour operators and scuttled in Congress just as the plan went out for bids, the light-rail system has stalled. Today, the canyon has a station (Canyon View Information Plaza) without a train, and the summer influx of cars creates congestion, noise, clouds of exhaust, and downright peevishness among frustrated drivers.