USA Today recently published an article detailing the most polluted U.S. national parks and one Colorado park was on the ‘top 10’ list.

According to the “Polluted Parks” report from the National Parks Conservation Association (NPCA), 97% of national parks suffer from significant or unsatisfactory levels of air pollution, and 98% suffer from haze pollution. Also, 96% include sensitive species and natural habitats harmed by sulfur and nitrogen deposition and ozone pollution.

The NPCA listed Rocky Mountain National Park (RMNP) as the ninth most-polluted U.S. national park, specifically looking at parks with ‘unhealthy air.’. RMNP is one of the U.S.’s most-visited national parks and is known for its natural beauty. Unfortunately, it is still threatened by pollution.

According to the National Park Service, vehicles, power plants, agriculture, fire, oil, gas, and more contribute to air pollution in RMNP. NPCA also reports that the boom in oil and gas production in Weld County has adversely affected RMNP, causing the park to fall out of compliance with the Clean Air Act.

Sequoia & Kings Canyon National Parks in California topped the list as the most polluted, with significant concerns regarding visibility, health, and nature.

Read the full report from NPCA here.