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the load is atmospheric deposition; and, smoke from homes heated with wood burning stoves and from slash burning may be the primary source of labile phosphorus measured in bulk precipitation samples. In 1983 a lakewide bloom of the noxious bluegreen alga Anabaena flos-aqua occurred for the first time in Flathead Lake since records began in 1902. The bloom was not severe and it has not reoccurred, but it did suggest that conditions in the lake were near a threshold beyond which major changes in the autotrophic community of the lake might be expected. Recent nutrient bioassays and analyses of long-term mass balance data have supported this inference (Stanford et al. 1983, 1990). Food Web Manipulation Since the turn of the century, 17 fish and 2 crustacean species have been purposefully introduced into the Flathead catchment, primarily by fishery managers. Most fishes and both crustaceans established viable populations and gradually immigrated widely within the catchment. Today only a very few lakes in Glacier National Park have entirely native food webs, owing to remote localities and presence of cascades, falls or other migration barriers that prevented invasion by nonnative species from waters downstream. These introductions had major impacts on native populations and dramatically restructured food webs in the lakes and streams throughout the catchment. Often effects cascaded through the food webs in ways that were unanticipated and sometimes involved both terrestrial and aquatic species. For example, the kokanee salmon (Oncorhynchus nerka) fishery has undergone extreme fluctuations since they were introduced into Flathead Lake in 1916. Kokanee population expanded rapidly after introduction and gradually replaced the native cutthroat trout as the dominant planktivore. Adfluvial kokanee from Flathead Lake spawned primarily in the outlet of McDonald Lake in Glacier National Park (Figure 3), where they attracted large numbers of migratory bald eagles (Haliaetus leucocephalus). When the kokanee spawners were abundant (> 150,000), so were eagles (> 700). In 1981, the nonnative crustacean Mysis relicta immigrated to Flathead Lake from intentional plants made in lakes upstream. Within 6 years numbers exceeded 125 m-2. Mysis feed on zooplankton near the lake surface at night and rest on the lake bottom during the day. Mysis have reduced zooplankton biomass in the lake by almost an order of magnitude. Kokanee are also dependent on zooplankton, but they prefer to stay near the lake surface, perhaps to avoid predation by piscivorous lake trout (Salvelinus namaycush, a nonnative species) and native bull charr. Thus, Mysis 13