The Sacramento River and its drainage basin were originally abundant in multiple avian and aquatic species, but modern-day development has thinned populations of many species, especially riverine. The river’s once-ample stretches of riparian zones and marshes, supported by its wide variations in flow, as well as the wetlands downstream in the Delta, have mostly been replaced by agricultural lands. The Sacramento supports 40–60 species of fish, and 218 types of birds. The basin is relatively abundant in endemic amphibian and fish species. It is surmised that between four and five million years ago, the Sacramento and Snake-Columbia River systems were somehow connected by a series of now-dry wetlands and river channels. Many of the fish in the present-day river are similar to those of the other, indicating a possible link sometime in the past. The Sacramento and San Joaquin also have the southermost runs of five species of anadromous fish.
The Feather River is the principal tributary of the Sacramento River, in the Sacramento Valley of Northern California. The river’s main stem is about 71 miles long. Its length to its most distant headwater tributary is about 220 miles. Its drainage basin is about 6,000 square miles. The main stem Feather River begins in Lake Oroville, where its four long tributary forks join together—the South Fork, Middle Fork, North Fork, and West Branch Feather Rivers. These and other tributaries drain part of the northern Sierra Nevada, and the extreme southern Cascades, as well as a small portion of the Sacramento Valley. The river’s drainage basin above Lake Oroville is 3,222 square miles, or about 83% of the whole.
The Yuba River is a tributary of the Feather River in the Sacramento Valley. It is one of the Feather’s most important branches, providing about a third of its flow. The main stem of the river is about 40 miles long, and its headwaters are split into North, Middle and South forks; the confluence of the former two is considered the beginning of the Yuba. The river drains about 1,339 square miles of the western slopes of the Sierra Nevada mountain range as well as a small portion of the Sacramento Valley.