Park staff has also monitored selected streams to determine water quality, temperature, flow, gradient, and resident salmonid populations. The native fish species of the lower Stehekin River and of Lake Chelan have been severely impacted by hydropower operations, natural catastrophic flooding and introduction of non-native aquatic species. The native sport fish included Lake Chelan cutthroat trout and bull trout. However, bull trout may be extinct in Lake Chelan and the Stehekin River. Activities that threaten natural resources include air pollution, overflights, acid precipitation, fish stocking, water pollution, hunting, mining, and administrative actions.
Baseline information is necessary to detect resource threats, trends, impacts and associated causes.
The Complex has about 245 natural lakes. Most of the natural high lakes were devoid of fish life because of natural barriers to fish migration. Currently over 75 high lakes support introduced populations of rainbow, cutthroat, brook and golden trout. Salamanders were the dominant, naturally-occurring aquatic vertebrate predator in the high lakes prior to stocking. A multi-year study is examining the effects of fish introductions on native fish communities.