Historically, native fish species lived only in the lower elevation reaches of the Kaweah, Kern, and Kings Rivers, typically below 6,000 ft (1,800 m) in elevation. As a result of the introductions of nonnative fish into high-elevation lakes, 550 of the parks' 3,500 previously fishless lakes, ponds, and marshes have self-sustaining populations of trout. Although trout are being removed from a subset of these lakes to restore the native yellow-legged frogs, hundreds of lakes will continue to support trout and provide recreational angling opportunities.