The Mad River is a river in upper Northern California. It flows for 95 miles (150 km) in a roughly northwest direction through Trinity County and then Humboldt County, draining a 497 square mile (1290 km²) watershed into the Pacific Ocean near Arcata-Eureka Airport in McKinleyville. The river's headwaters are in the Coast Range near South Kelsey Ridge.
The river has one dam and is free-flowing for 85 percent of its length. Matthews Dam, about one third of the way down the river from its source, forms Ruth Lake. The dam is owned by Humboldt Bay Municipal Water District, which serves Eureka, Arcata, Blue Lake and several unincorporated communities. The reservoir can hold 48,000 acre feet (59,000,000 m³) of water.
Like many rivers in this area of the state, the watershed's greatest problem is erosion causing excessive sediment buildup in the river and it tributaries. The main causes of the erosion are excessive road building and logging, especially historical logging practices. In addition, the removal of riparian vegetation, which also increases erosion, and urbanization are also causing decreased water quality.
The upper half of the river is inside the Six Rivers National Forest, but the vast majority of the river flows through private land, even in the national forest. About 64 percent of the land is used for timber production. Simpson Timber Company is by far the largest landowner in the watershed, with about 42 percent of all land. The next largest landownders are R. Emmerson and Pacific Lumber Company, with 3 and 2 percent respectively. There are quite a few ranchers and lumber companies that own smaller, but still sizable, parcels. Private residences, open space and parks make up most of the rest.
The Mad has become known for its excellent winter steelhead, due in large part to the operation of the Mad River Fish Hatchery. The hatchery is also working to improve the chinook runs on the river. This past season saw an excellent return of Kings on the river. The hatchery is located about one mile southeast of the town of Blue Lake on the south side of the river. You can visit and see steelhead and chinook fry and smolts that will be introduced back into the river.
The best fishing on the Mad lies from the hatchery to the mouth. This area provides good access for waders and bank fishermen. The area above the hatchery has limited access due to private property and few roads, however some good areas can be accessed by wading upstream. This area offers a chance at some wild Mad River Steelhead.