from the industrialized region around Puget Sound and the Fraser River Valley of British Columbia. These pollutants deposit onto plants and glaciers and are then carried by rainfall or ice melt and dispersed into rivers and lakes. The industrialized regions around Puget Sound and the Fraser River Valley have had a more noticeable negative impact on water and air quality than at Mount Rainier National Park well to the south due to the prevailing winds. Lakes at higher elevations show a higher level of acidity due to this phenomenon; the current and long-term impact on the ecosystem of the park has not yet been fully assessed. Mercury and toxins from pesticides have been detected in the park, as has ozone; these have not been demonstrated to be at sufficient concentrations to greatly impact the ecosystem. Sulfur, nitrogen dioxide and ozone from factories and automobile emissions as well as increased dust and fine particulates from sources such as farming and construction are dispersed into the atmosphere, reducing long-range visibility. Visibilities of up to have been reduced to less than on the worst days due to the increased haze. Climate change will impact the temperatures of high altitude lakes and streams, which in turn will have an effect on the fish that can thrive in these waters. Retreating glaciers reduce the amount of glacial ice melt available in warmer months that kept streams and lakes cold, even in late summer. Attractions North Cascades National Park is approximately northeast of Seattle. Nearly all of the national park is protected as the Stephen Mather Wilderness and it is "one of the premier wilderness parks" in the lower-48 states". Unlike some national parks, there is no entrance fee at North Cascades, and hiking trailheads accessed by vehicle do not require a parking pass; trailheads on some national forest properties adjacent to the park may require a pass. Mount Shuksan, in the northwest corner of the park, is often photographed, and at is the second highest peak in the park. Camping, hiking and bicycling Hikers and backpackers often visit Cascade Pass in the southwestern section of the southern unit of the park, which was used as a travel route by Native Americans. The pass can be reached by a hiking trail accessed from a parking lot at the end of a gravel road that starts at Marblemount. There are nearly of hiking trails in the park.