The Eel River drains an area of 3,684 square miles (9,540 km²), the third largest watershed entirely in California, after those of the San Joaquin River and the Salinas River.
The Colorado, Sacramento, and Klamath River systems are larger, but their drainage areas extend into neighboring states as well.
The Eel River system extends into five California counties – Glenn, Humboldt, Lake, Mendocino, and Trinity.
The main stem traverses four counties, excepting Glenn.
The majority of the watershed is located within Mendocino and Humboldt Counties.

The Eel's major tributaries – the North Fork, Middle Fork, South Fork and Van Duzen Rivers, drain 286 square miles (740 km²), 753 square miles (1,950 km²), 689 square miles (1,780 km²), and 420 square miles (1,100 km²), respectively.
The Middle Fork drains the greatest area of all the tributaries, but the South Fork is longer, and carries the most water because of the higher rainfall in its basin.

The Eel River watershed is located entirely in the California Coast Ranges.
The topography creates a general drainage pattern that runs from southeast to northwest, except in the Middle Fork basin and the Eel headwaters, where water runs from east to west.
The watershed is bordered on the north by the basin of the Mad River, on the east by that of the Sacramento River, on the west by that of the Mattole River, and on the south by those of the Russian River and Ten Mile River.
Major centers of population on the river include Willits, Garberville, Redway, Scotia, Rio Dell, Fortuna, and Ferndale.
Minor communities include Laytonville, Branscomb, Cummings, Leggett, Piercey, Benbow, Phillipsville, Myers Flat, Shively, and Pepperwood.
The river's relatively large estuary and delta, which includes the Salt River tributary and related creeks, is located just one low ridge south from Humboldt Bay and 12 miles (19 km) south of Eureka, the main city for the entire region.

Since the 19th century, logging activity in the watershed has loosened soil and destabilized aquifers, reducing the river's base flow, although the watershed is slowly recovering.
Logging, grazing and other resource exploitation activities and their accompanying environmental changes have also increased the intensity of flood and drought.
Prior to 2011, the Eel River basin consisted of 65.1% forest, 12.2% shrubland, and 19.2% grassland, with just 1.9% agricultural and 0.2% developed urban.
The human population of the watershed is about 32,000 – less than 10 people per square mile (26/km²).

In the 20th century, much of the watershed area was included under state parks and national forest, including Six Rivers National Forest, Yolla Bolly-Middle Eel Wilderness, and Humboldt Redwoods State Park.
A total of 398 miles (641 km) of the Eel River and its major tributaries are protected under the National Wild and Scenic Rivers system, with 97 miles (156 km) classed as Wild, 28 miles (45 km) as Scenic, and 273 miles (439 km) as Recreational.
About 155 miles (249 km) of the main stem are designated, from the mouth to a point just below Cape Horn Dam.
The Middle Fork is also Wild and Scenic from its confluence with the Eel to the boundary of the Yolla Bolly–Middle Eel Wilderness.
The South Fork is designated from its mouth to the Section Four Creek confluence, the North Fork from its mouth to Old Gilman Ranch, and the Van Duzen River from its mouth to Dinsmore Bridge.
The Eel River drains an area of 3,684 square miles (9,540 km²), the third largest watershed entirely in California, after those of the San Joaquin River and the Salinas River. The Colorado, Sacramento, and Klamath River systems are larger, but their drainage areas extend into neighboring states as well. The Eel River system extends into five California counties – Glenn, Humboldt, Lake, Mendocino, and Trinity. The main stem traverses four counties, excepting Glenn. The majority of the watershed is located within Mendocino and Humboldt Counties.
The Eel's major tributaries – the North Fork, Middle Fork, South Fork and Van Duzen Rivers, drain 286 square miles (740 km²), 753 square miles (1,950 km²), 689 square miles (1,780 km²), and 420 square miles (1,100 km²), respectively. The Middle Fork drains the greatest area of all the tributaries, but the South Fork is longer, and carries the most water because of the higher rainfall in its basin.
The Eel River watershed is located entirely in the California Coast Ranges. The topography creates a general drainage pattern that runs from southeast to northwest, except in the Middle Fork basin and the Eel headwaters, where water runs from east to west. The watershed is bordered on the north by the basin of the Mad River, on the east by that of the Sacramento River, on the west by that of the Mattole River, and on the south by those of the Russian River and Ten Mile River. Major centers of population on the river include Willits, Garberville, Redway, Scotia, Rio Dell, Fortuna, and Ferndale. Minor communities include Laytonville, Branscomb, Cummings, Leggett, Piercey, Benbow, Phillipsville, Myers Flat, Shively, and Pepperwood. The river's relatively large estuary and delta, which includes the Salt River tributary and related creeks, is located just one low ridge south from Humboldt Bay and 12 miles (19 km) south of Eureka, the main city for the entire region.
Since the 19th century, logging activity in the watershed has loosened soil and destabilized aquifers, reducing the river's base flow, although the watershed is slowly recovering. Logging, grazing and other resource exploitation activities and their accompanying environmental changes have also increased the intensity of flood and drought. Prior to 2011, the Eel River basin consisted of 65.1% forest, 12.2% shrubland, and 19.2% grassland, with just 1.9% agricultural and 0.2% developed urban. The human population of the watershed is about 32,000 – less than 10 people per square mile (26/km²).
In the 20th century, much of the watershed area was included under state parks and national forest, including Six Rivers National Forest, Yolla Bolly-Middle Eel Wilderness, and Humboldt Redwoods State Park. A total of 398 miles (641 km) of the Eel River and its major tributaries are protected under the National Wild and Scenic Rivers system, with 97 miles (156 km) classed as Wild, 28 miles (45 km) as Scenic, and 273 miles (439 km) as Recreational. About 155 miles (249 km) of the main stem are designated, from the mouth to a point just below Cape Horn Dam. The Middle Fork is also Wild and Scenic from its confluence with the Eel to the boundary of the Yolla Bolly–Middle Eel Wilderness. The South Fork is designated from its mouth to the Section Four Creek confluence, the North Fork from its mouth to Old Gilman Ranch, and the Van Duzen River from its mouth to Dinsmore Bridge.
Eel River (California)