As summer tourism season heats up, the U.S. National Parks system typically readies for its biggest crowds of the year, but some parks that usually see large numbers of Canadian visitors are starting to notice a worrying trend that could have a major impact this year.

Since its founding on August 25, 1916, the U.S. National Park Service has assembled 419 protected units, of which 62 hold the “national park” designation. To visit all 63 of these treasures one would need to travel to 29 states and two U.

Earth Day also falls during National Park Week. Celebrated for 55 years, one billion people in 193 countries host events and celebrations of the planet, its resources and our commitment to protect it. Many of our national parks will have special Earth Day demonstrations of earth science or discussions of the latest environmental concerns.