The Kern River formerly emptied entirely into now dry Buena Vista Lake at the southern end of the Central Valley. The river has been almost entirely diverted for irrigation, recharging aquifers and the California Aqueduct, although some water empties into Lake Webb and Lake Evans, two small lakes in a portion of the former Buena Vista Lakebed. The lakes were created in 1973 for recreational use. The lakes hold 6,800 acre-feet combined. Crops are grown in the rest of the former lakebed. In extremely wet years the river will reach the Tulare Lake basin through a series of sloughs and flood channels.
At Kernville the river emerges from its narrow canyon into a widening valley where it is impounded in Lake Isabella, a reservoir formed by Isabella Dam. The area was once known as Whiskey Flat, the former location of the town of Kernville. The South Fork Kern River joins in Lake Isabella. Like the North Fork, the South Fork rises in Tulare County and flows mainly south, through Inyo National Forest. After entering Kern County the South Fork curves to the west and flows into Lake Isabella.
Below Isabella Dam the Kern River flows southwest through a spectacular rugged canyon along the south edge of the Greenhorn Mountains, emerging from mountains east of Bakersfield, the largest city on the river. In the Kern's lower course downstream from Bakersfield the river is highly diverted through a series of canals to irrigate the farms of the southern San Joaquin Valley and provide municipal water supplies to the City of Bakersfield and surrounding areas. In this region near Bakersfield the Kern River once spread out into vast wetlands and seasonal lakes.
The Friant-Kern Canal, constructed as part of the Central Valley Project, joins the river about four miles west of downtown Bakersfield.
The Kern River is one of the very few rivers in the Central Valley which does not contribute water to the Central Valley Project (CVP). However, water from the CVP, mainly the Friant-Kern Canal, will be deposited for water storage in the aquifers.
The Kern River Oil Field is adjacent to the river on the north, just before the river flows into Bakersfield. The large oil field, on low hills which rise gradually into the Sierra foothills, formerly allowed much of its produced water to drain directly south into the river. However, modern environmental regulation ended this practice, and the contaminated water is now cleaned at water treatment plants and used to irrigate farms in the valley to the west.
Formerly the river flowed an additional south through a now-dry distributary to Arvin, where it formed the seasonal Kern Lake, which would grow to cover about 8,300 acres during wet periods. Water from Kern Lake would then flow west through Buena Vista Slough into Lake Buena Vista, another seasonal lake that reached sizes of about 4,000 acres. Another channel of the Kern RIver flowed from the Bakersfield area southwest directly to Buena Vista Lake. In periods of high runoff, Buena Vista Lake overflowed and joined other wetlands and seasonal lakes in a series of sloughs that drained north into the former Tulare Lake, which would sometimes overflow into the San Joaquin River.
Due to water diversion and Isabella Dam the Kern River's discharge changes considerably over its length. The highest mean annual flows occur just downriver of Isabella Dam, but because the dam serves to regulate the flow of water the highest daily discharges occur above the dam on the North Fork section of the Kern River. The USGS stream gage on the North Fork Kern River has recorded an average annual mean discharge of 806 cubic feet per second (ft³/s) and a maximum daily discharge of 33,600 ft³/s, and the gage on the South Fork Kern River shows an average annual mean of 123 ft³/s and a maximum daily discharge of 14,000 ft³/s. In contrast the first stream gage below Isabella Dam has recorded an average annual mean of 946 ft³/s but a maximum daily discharge of only 7,030 ft³/s. Due to water withdrawals the three stream gage stations below Isabella Dam show a dramatically decreasing discharge. At the last gage, near Bakersfield, the river's average flow is only 312 ft³/s.
The river was named by John C. Frémont in honor of Edward M. Kern in the 1830s who, as the story goes, nearly drowned in the turbulent waters. Kern was the topographer of his third expedition through the American West. Before this, the Kern River was known as the "Rio Bravo de San Felipe" as named by Spanish missionary explorer Fr. Francisco Garces when he explored the Bakersfield area in 1776. Gold was discovered along the upper river in 1853. The snowmelt that fed the river resulted in periodic torrential flooding in Bakersfield until the construction of the Isabella Dam in the 1950s. These floods would periodically change the channel of the river. Since the establishment of Kern County in 1866 the main channel has flowed through what is the main part of downtown Bakersfield along Truxtun Avenue and again made a south turn along what is Old River Road. Many of the irrigation canals that flow in a southerly direction from the river actually follow the old channels of the Kern River, especially the canal that flows along Old River Road. The irrigated region of the Central Valley near the river supports the cultivation of alfalfa, carrots, fruit, and cotton, cattle grazing, and many other year-round crops. In 1987 the United States Congress designated 151 mi (240 km) of the Kern's North (Main) Fork and South Fork as a National Wild and Scenic River.
In recent years the river has become controversial because of attempts by the City of Bakersfield to retain water in the river channel all year round for recreation and the recharging of the water tables from which it draws its drinking water supply. The attempts have resulted in conflicts with established agricultural interests in the Central Valley which depend heavily on the river as a supply of irrigation water. However, the river recently has been allowed to flow its normal dry course due to structural problems in the Isabella Dam. The increased flow reduces stress on the dam.
The deep canyon of the river northeast of Bakersfield is a popular location for fly fishing and particularly famous for whitewater sports including whitewater rafting, whitewater kayaking, and riverboarding.
The Kern is also well known for its danger, and is sometimes known as the "Killer Kern". A sign at the mouth of Kern Canyon warns visitors, "Danger. Stay Out. Stay Alive" and tallies the deaths since 1968; as of November 3 2007 the count was up to 240. Bakersfield-born Merle Haggard's song Kern River recounts just such a tragedy. The number of deaths is currently 250. Most of the people who die in the Kern river are campers and amateur recreational users who enter the water without proper life vests. Fewer than 2% of the deaths on the Kern have occurred on commercial raft trips. If you are not an expert whitewater athlete or professional, do not enter the water above the depth of your knees without wearing proper a proper floatation vest, and never tie a person or an animal to a rope in or near the the river. The recreational grade rafts which can be bought in department stores are not suitable and are not safe for use in the Kern river.
The Kern is nevertheless a popular place for camping, hiking, fishing and recreational vacation. Of particular interest to fisherman are the Little Kern Trout and the Golden Trout.
Below the canyon the Kern River drops an average of 16 feet per mile until it reaches the Kern River Oil Field and begins to meander along flat land into and through the city of Bakersfield. It is a popular summer pastime to float down the river on inner tubes in the Class II sections near Bakersfield far outside of the Kern Canyon. This activity is often done in groups and beer is taken along in an ice chest rigged to float alongside, though highly dangerous.