Bull trout (Salvelinus confluentus) and dolly varden (Salvelinus malma) were once considered to be the same species. They have been separated because of genetic, morphological, and behavioral differences. In general, bull trout are the "inland" form, while dolly varden migrate to the ocean (where they spend much of their adult life) and return to reproduce in freshwater. This makes the dolly varden an anadromous fish, similar in behavior to salmon.

Once found in most major river systems in the Pacific Northwest, bull trout distribution has been significantly reduced over the past 30 years and many local extinctions have occurred. Oregon's Klamath River Basin represents the southern Limit of present day bull trout distribution. The Klamath populations are genetically distinct from other populations in the region and are now restricted to cold headwater streams. Habitat degradation and introduction of non-native fish species are believed to be the primary causes for the decline. Bull trout have been Listed as a Category 2 Species (candidate species under the Endangered Species Act of 1973) by the U.S. Fish and Wildlife Service (USFWS) and is listed as a sensitive species by the State of Oregon.

Bull trout were probably the only fish species present in Sun Creek, a high elevation, second order stream, prior to early introductions of non-native salmonids. National Park Service (NPS) and Oregon Department of Fish and Wildlife (ODFW) records indicate repeated stocking of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) in Sun Creek between 1928 and 1971. The only park-wide stream survey conducted during this period took place in 1947. A seasonal naturalist named Orthello Wallis (who later became the first aquatic biologist ever employed by the NPS) found bull trout, rainbow trout, and brook trout in Sun Creek.

A resurvey of Sun Creek was made in the summer of 1989 to investigate the distribution and abundance of fish relative to habitat characteristics. The survey was funded as part of Klamath River Basin water rights adjudication. Sun Creek was surveyed from its headwaters to the park boundary. Bull trout, brook trout, and hybrids from the two species were collected. No rainbow trout were collected in the portion of Sun Creek within the park and may no longer exist in the stream.

Investigators observed that habitat utilization by bull trout and brook trout was very similar. Competition and hybridization with brook trout have probably reduced the distribution of bull trout in Sun Creek. Bull trout were restricted to a 1.9 km reach of the stream and the total number of adult bull trout was estimated at 130 fish. Such a low population density is alarming, since it suggests that local extinction could occur within the next few years.

The NPS is developing a bull trout management program whose goals are to remove brook trout from Sun Creek, build a barrier to prevent re-invasion, and to re-establish a self-sustaining population of bull trout in Sun Creek within Crater Lake National Park. During 1991, park staff convened a "Bull Trout Recovery Team" to develop recommendations on how to best achieve these goals. It consisted of representatives from the NPS, USFWS, ODFW, U.S. Forest Service, California Department of Fish and Game, and Oregon State University. A final report from the group is expected in early 1992 and will form the basis for the first active fish management project ever undertaken in the park. An environmental assessment will be available for public comment before any management action is taken.

Visitors should note that fishing for bull trout in Crater Lake National Park and throughout south central Oregon is prohibited by state law. Bull trout within the park are also protected by federal regulations. Fishing for other species in most park streams is permitted. Copies of fishing regulations are available at the park's visitor centers. Fishing in Crater Lake for kokanee salmon (Oncorhynchus nerka) and rainbow trout (Oncorhynchus mykiss) is allowed. No state license is required and fishing on the lake has been good in recent years.