Lahontan Cutthroat now being planted in the West Fork of the Carson River

The Lahontan cutthroat is native to the drainages of the Truckee River, Humboldt River, Carson River, Walker River, Quinn River and several smaller rivers in the Great Basin of North America. These were tributaries of ancient Lake Lahontan during the ice ages until the lake shrank to remnants such as Pyramid Lake and Walker Lake about 700 years ago, although Lake Tahoe -- from which the Truckee flows to Pyramid Lake -- is still a large mountain lake.
Lahontan cutthroats evolved into a large (up to 1 metre (39 in)) and moderately long-lived predator of chub, suckers, and other fish as long as 30 or 40 centimetres (16 in). The trout was able to remain a predator in the larger remnant lakes where prey fish continued to flourish, but upstream populations were forced to adapt to eating smaller fish and insects. Some experts consider O. c. henshawi in the upper Humboldt River and tributaries to be a separate subspecies (the "Humboldt cutthroat trout"), adapted to living in small streams rather than large lakes.
The record size cutthroat trout of any subspecies was a Lahontan caught in Pyramid Lake weighing 41 pounds (18.6 kg), although there is anecdotal and photographic evidence of even larger fish from this lake.