Rough-skinned newts (Taricha granulosa) within the Crater Lake caldera have been proposed as an endemic subspecies, the Mazama newt (T. granulosa mazamae), and preliminary genetic analyses affirm that the population is distinct and isolated from related newts outside the caldera.
Signal crayfish (Pacifastacus leniusculus) were introduced into Crater Lake around 1914 and have since expanded to fill over half of shoreline habitat in the lake.
Observational evidence collected by park scientists suggests that the invasive crayfish are continuing to expand and have reduced the distribution of endemic newts. Newts remain in areas that crayfish have not yet invaded, but are almost entirely absent from areas occupied by crayfish.
Introduced crayfish in other systems have been documented to cause rapid declines in abundance of native salamanders.
If no action is taken at Crater Lake, crayfish ultimately may cause extinction of the unique Mazama newt.