Heavy snows and a high risk of avalanches due to the steep terrain, especially on the western slopes, severely limit visitation in the winter. Most access to the park is from State Route 20, which follows the Skagit River, though even this road is closed for months at a time in the winter. Most of the plant and animal species native to the park region are still found there, though climate change and pollutants from industrialized regions to the west pose risks to the environment. The park has one of the earliest and longest lasting research programs dedicated to studying climate change, primarily through examining the effects of glacial retreat.