Crater Lake is located in a caldera formed over 7,700 years ago by the collapse of Mount Mazama. It is the deepest lake in the United States, reaching nearly 1,943 feet. The water is known for its extraordinary clarity and purity. This unique geological history and the absence of natural inlet or outlet streams suggest an isolated aquatic environment untouched by external life.
Current Status of Fish in the Lake
The surprising answer is that Crater Lake does contain fish. However, the lake was originally barren of native species due to its isolated, high-altitude formation. The fish currently inhabiting the deep, cold waters are entirely non-native, introduced by humans beginning in the late 19th century. These populations have since become self-sustaining through natural reproduction in the lake’s nearshore areas.
The History of Fish Stocking
The introduction of fish began in 1888 with William G. Steel, a key figure in establishing Crater Lake National Park. Steel aimed to enhance the lake’s recreational appeal and strengthen the rationale for its protection. His initial attempts involved transporting fingerling trout in buckets up the steep caldera walls, which had limited success.
A formal stocking program began around the turn of the century and continued for over five decades. Between 1888 and 1941, approximately 1.8 million fish, consisting of at least seven different species of salmonids, were introduced. This extensive effort was conducted by various agencies focused on creating a sport fishery. The practice was halted in 1941 once researchers determined that certain introduced species had established self-sustaining populations.
Species That Survive in Crater Lake’s Waters
Despite the large number of fish introduced, only two species successfully adapted to the lake’s challenging environment and persist today. These survivors are the Rainbow Trout (Oncorhynchus mykiss) and the Kokanee Salmon (Oncorhynchus nerka). The Kokanee Salmon is the landlocked, non-migratory form of the Sockeye Salmon. The lake’s water is extremely cold and classified as oligotrophic, meaning it is relatively low in nutrients and biological productivity.
The success of these two species is due to their ability to exploit different niches within the limited food web. Kokanee Salmon are generally the most abundant, feeding primarily on zooplankton in the open water column. Rainbow Trout are less numerous but tend to be larger, occupying nearshore areas where they consume aquatic insects and small invertebrates. Their differing diets allow them to co-exist without excessive competition for the lake’s scarce resources. Researchers have documented Rainbow Trout reaching up to 26 inches in length, demonstrating that the environment can support healthy growth.
Ecological Management and Policy
The National Park Service (NPS) currently manages the non-native fish population with a policy of containment rather than active removal. Since the fish are established and stocking efforts ceased in 1941, the focus is on preventing further ecological damage and outside introductions. Fishing is permitted and encouraged as a means of naturally controlling the non-native population, and no fishing license is required within the park boundaries.
Anglers face no size restrictions or catch limits for the Rainbow Trout and Kokanee Salmon taken from the lake. This unusual approach, which does not mandate catch-and-release, reflects the non-native status of the fish. To protect the lake’s purity and prevent the introduction of new organisms, only non-organic artificial lures may be used, and cleaning fish in the lake is strictly prohibited.
Ecological Ramifications
The presence of these fish has had ecological ramifications. This includes the historical introduction of Signal Crayfish (Pacifastacus leniusculus) as a forage food. The crayfish population has subsequently expanded, threatening the endemic Mazama newt (Taricha granulosa mazamae) and potentially compromising the lake’s water clarity.