The Ventura River watershed encompasses 226 square miles (590 km2) consisting of steep mountains and foothills, with altitudes ranging from 6,010 feet (1,830 m) to sea level. Valley floors are home to communities and farms. Conditions in much of the watershed remain natural and undeveloped, with 57% of its land area in protected status. Most of the watershed’s primary streams and drainages are unchannelized, though two dams—Casitas and Matilija—and three levees—Ventura River, Casitas Springs, and Live Oak—have modified natural hydrologic patterns.
The northern half of the watershed lies within Los Padres National Forest. The watershed’s southern half includes two cities and a number of unincorporated communities. The City of Ojai lies entirely within the watershed, 13-mile inland (21 km) at an elevation of 746 feet (227 m). Thirteen percent of the City of Ventura lies within the watershed, adjacent to the coast and the lower stretch of the Ventura River. Developed land (excluding grazing) comprises only about 13% of the total land area in the watershed. Agriculture is the dominant land use. Citrus and avocados are the primary irrigated crops grown, and a significant area of land is used for cattle grazing.
The population of the watershed is relatively small and the rate of growth low. The population is approximately 44,140, which represents just 5.4% of Ventura County’s population (as of 2010 Census). The population is 58% white, 37% Hispanic or Latino, 2% Asian, and 3% other races. Income varies widely, and several areas qualify as disadvantaged or severely disadvantaged communities.
Rainfall varies geographically, seasonally, and from year to year. Median annual precipitation is 14.12" (in the lower watershed), 19.20" (in the middle watershed), and 28.74" (in the upper watershed). Cycles of drought and flood are the norm. Since 1906, 67% of the years have had less than average rainfall. Many parts of the stream network are typically dry during much of the year. Surface water readily disappears underground in some stream reaches (segments); in others, groundwater regularly feeds streamflow.
Rainfall in the Matilija Wilderness, the river’s headwaters, is the highest in Ventura County, with average annual rainfall that is over twice that of rainfall at the coast. The steep terrain of the Ventura River watershed, coupled with intense downpours that can occur in its upper portions, result in flash flood conditions where floodwaters rise and fall in a matter of hours. Major or moderate floods have occurred once every five years on average since 1933.
The most damaging riverine flood recorded in the Ventura River watershed occurred in 1969. The watershed above Ojai received a staggering 43 inches of rain in nine days in January. The floodwaters and associated debris rolled down out of the mountains, flooding homes in Casitas Springs and Live Oak Acres. Much agricultural land, primarily citrus groves, was seriously damaged or destroyed. All over Ventura County, transportation facilities, including roads, bridges, and railroad tracks, were damaged. The wastewater treatment plant below Foster Park was severely damaged and dumped raw sewage into the Ventura River. In addition, sewer trunk lines were broken along the Ventura River and San Antonio Creek. Untreated sewage polluted the river and beach. The capacity of the Matilija reservoir was significantly reduced by siltation from the flood.
Limited land development and large areas of protected habitat in the Ventura River watershed help support surface water that is relatively clean compared with more developed areas in the region. However, all of the watershed’s major waterbodies are on the Clean Water Act Section 303(d) list of impaired waterbodies. Surface waters are impaired for a number of factors, including trash, algae, water diversion/pumping, eutrophic conditions, low dissolved oxygen, nitrogen, fish barriers, coliform, bacteria, mercury, and total dissolved solids.
Unlike almost all of its neighbors in southern California, Ventura River watershed is 100% dependent on local water supplies. Lake Casitas serves as the major surface water supply reservoir in the watershed and groundwater is heavily relied upon. On average, surface water comprises about 55% of the water recovered from the watershed and groundwater comprises about 45%.
Cycles of drought and flooding occur regularly. Annual rainfall in downtown Ojai has ranged from a low of seven inches to a high of 49 inches—a sevenfold variation. Because the annual amount of rainfall received is highly variable, water supplies must be managed with caution.
Two small coastal watersheds—the North Ventura Coastal Streams watershed and the Buenaventura watershed—flank the Ventura River watershed’s lower section and are dependent on its water. Water from the Ventura River watershed is used to irrigate avocado orchards in the North Ventura Coastal Streams watershed and serves a significant population in a portion of the Buenaventura watershed that lies within the City of Ventura.
The flow of the Ventura River and its tributary Coyote Creek have been reduced by the completion of Casitas Dam, which forms Casitas Reservoir. The dam is on Coyote Creek about 2 miles upstream of the junction with the Ventura River. The Robles Diversion Dam was constructed on the Ventura River in 1958 to divert up to 107,800 acre-feet of water per year through a four-and-a-half mile canal to Casitas Reservoir. About 40% of the total water in Lake Casitas is supplied from high winter flows in the Ventura River. Casitas Municipal Water District sells water to both domestic and agricultural customers.
The Matilija Creek tributary is also dammed, by Matilija Dam. Completed in 1948, it was built to store 7,000 acre feet (8,600,000 m3) of water, but sediment has reduced its capacity by 90%. Many groups, including some governmental ones, are working towards the removal of the dam. On November 8, 2007, the 110th Congress overturned President Bush's veto of a bill delegating approximately $89.7M to the project.
The watershed’s rugged topography, largely undeveloped status, and Mediterranean climate combine to make for an area of exceptional biodiversity. It supports a diverse array of natural habitats, including grassland, coastal sage scrub, chaparral, oak woodlands and savannas; coniferous woodlands; riparian scrub, woodlands and wetlands; alluvial scrub; freshwater aquatic habitats; estuarine wetlands; and coastal cobble, dune and intertidal habitats. The Ventura River estuary, at the mouth of the Ventura River, is an exceptionally valuable wetland habitat and ecological resource in the watershed.
The watershed is home to numerous protected species and habitats, including 137 plants and animals protected at either the federal, state, or local level. The federally endangered southern California steelhead (listed in 1997) is of particular importance, given the watershed’s often dry and always variable climate. The steelhead found in the Ventura River are part of the Southern California Steelhead Distinct Population Segment (DPS) were listed as federally endangered. Genetic analysis of the steelhead trout (Oncorhynchus mykiss) in the Ventura river watershed (both above and below Matilija Dam) has shown them to be of native and not hatchery stocks.
The Ventura River Preserve, owned by the Ojai Valley Land Conservancy (OVLC), protects 1,600 acres (650 ha) of land in and adjacent to the Ventura River, including 3 miles (4.8 km) of the river. Additional land in and adjacent to the river is protected by OVLC, along with Ventura Hillsides Conservancy, Ventura County Watershed Protection District, Ventura County Parks, and the City of Ventura.
Removing Matilija Dam, in part to return access to the steelhead to spawning habitat, is a major project that is underway in the Ventura River watershed. The watershed is also challenged by invasive, non-native species, such as Arundo donax.
Environmental Protection Agency became involved in August 2012 with the abandoned USA Petrochem petroleum refinery which is situated within the 100-year floodplain of the Ventura River. The EPA determined there had been discharge to navigable waters of the United States in violation of the Clean Water Act. Their site assessment found that there were numerous leaking pipelines, leaking tanks and leaking production vessels throughout the property. They issued an order that the site must be cleaned up or daily fines would be sought from the owner. The site was also out of compliance with Los Angeles Water Quality Control Board’s Ventura River Estuary Trash Total Maximum Daily Load. Encampments built in the river bottom by homeless people were the main problem. In 2015, the site owner agreed to remove all machinery and equipment, which would complete the cleanup of the plant that closed around 1985.
The Ventura River Parkway Trail was built on a abandoned railroad spur (CA_VEN-1109H) that was constructed by the Ventura and Ojai Valley Railroad in 1898 and acquired by Southern Pacific in 1899. The trail, that runs along the easterly bank of the river, was designated a National Recreation Trail in 2014. The "Ventura River Trail" part of the trail (completed in 1999) extends from the coast to Foster Park, and the "Ojai Valley Trail" part (completed in 1987) extends from Foster Park into the City of Ojai. The 15.8-mile trail (25.4 km), with the steady grade of the former Southern Pacific Railway right-of-way, is very popular with bicyclists, as well as walkers and horseback riders (on the Ojai Valley Trail segment). As of 2015, the vision of a “Ventura River Parkway,” a network of trails, vista points, and natural areas along the river, is being actively pursued by a coalition of stakeholders.
State Route 33 also roughly parallels the river through the Ventura River Valley. A portion of SR 33, north of the SR 150, is officially designated as a state scenic highway, and the entire Ventura River Valley section is eligible for the designation.
The watershed is a recreation destination for hikers, walkers, bikers, surfers, campers, fishermen, boaters, backpackers, equestrians, and birders, as well as artists, spiritual seekers, and students of natural history. Many local organizations are committed to providing the public with access to nature and nature-based recreation opportunities. Camping in the Ventura River bottom, which is dry most of the year, was outlawed by the Ventura City Council in 1995 after floods killed one man and prompted the evacuation of 12 other people near the Main Street bridge.
The Ventura River Watershed Council, which includes government agencies, nonprofit groups, businesses, community groups, and individuals, prepared a watershed management plan. Approved in 2015, this comprehensive plan proposed ways to improve the health and sustainability of the watershed.