The San Juan River provides habitat for at least eight native fish species – cutthroat trout, roundtail chub, speckled dace, flannelmouth sucker, bluehead sucker, mottled sculpin, Colorado pikeminnow, and razorback sucker, with a possible ninth, bonytail chub. The latter three are considered endangered under the Endangered Species Act of 1973, and are rarely found in the San Juan River today, if at all. With the exception of trout and dace, which inhabit clear, cold mountain streams in the headwaters, the native fishes are mostly adapted to the warm, shallow and silty characteristics of the lower San Juan. The San Juan cutthroat trout, a unique lineage of cutthroat trout endemic to the river and its tributaries, was considered extinct until its rediscovery in 2018. In addition, about 23 non-native fish species have been introduced to the San Juan River watershed. The common carp and channel catfish have become widespread in the lower reaches of the San Juan River. In the "tailwater" reach below Navajo Dam, introduced rainbow and brown trout thrive in the cold and stable flows released from the dam. Rainbow and brown trout have also proliferated in the headwaters of the San Juan River above Navajo Lake.