Each year over a thousand climbers attempt Alaska's 20,320-foot Mount McKinley inside Denali National Park and Preserve. It is one of the seven highest peaks of the seven continents. Starting next year, for safety and to protect the mountain, the National Park is limiting the number of climbers to 1,500 a year. Since 1903, McKinley has been attempted by 30,049 climbers with over half reaching the summit. Ninety-five climbers have died trying, including 11 in 1992. The large number of climbers spending time on Denali creates another problem: human waste. This is a common problem on popular Peaks and elsewhere in North America it is quite common to have to apply for a permit before you climb.
From the very big to the very small and back in the UK discussions are under way to restrict access at popular climbing areas like the Stanage Planatation where the increase in the number of climbers bouldering is causing erosion problems. A voluntary ban may be implemented here to give recent restoration efforts by climbers a chance to grow back. See this discussion on the UKClimbing.com forums.