A few hundred years ago a massive landslide blocked this channel, and Clear Lake found a new outlet to the Sacramento River.

Cold Creek flows year round, while the upper part of East Fork Russian River used to dry up in the summer leaving isolated pools along its course.

The section of the river that flows through the mountains between Potter Valley and Lake Mendocino includes stretches of white water that are challenging for kayakers and rafters.

[9] In a period of very low water in September 1905 the East Fork Russian River had a discharge of 2.2 cu ft/s (3.7 m3/min).

At this point the maximum discharge of the East Fork Russian River before regulation by Lake Mendocino was 13,300 sq ft/s (74,000 m2/min), recorded on 21 December 1955.

The East Fork of the Russian River has a youthful topography in this section, flowing with a high gradient through a V-shaped gorge.

Cold Creek flows at a much lower gradient, as is shown by the size of stones in its bed, and has a distinct flood plain and also a terrace.

[19] Before the Eel River water was diverted, the East Fork would nearly dry up in July, August and September.

A flour mill in Coyote Valley had water to drive its wheel carried from Cold Creek, which runs year round, along 1.5 mi (2.4 km) of flume.

The concrete gravity and earth filled Cape Horn Dam was built to impound a reservoir called Lake Van Arsdale on the Eel River.

A tunnel 8 ft (2.4 m) in diameter lined with redwood timbers was excavated for more than 1 mi (1.6 km) south to emerge above the northern end of Potter Valley.

The water then fell through a penstock with vertical elevation of more than 450 ft (140 m) to the Potter Valley Powerhouse, which came online in April 1908 to deliver 4 MW.

[21] At first the powerhouse only ran at full capacity in the winter, and had to shut down completely in summer due to lack of water.

In 1920 work started on Scott Dam, a large concrete ogee gravity structure 12 mi (19 km) upstream from Van Arsdale which collects water from the upper 7.3% of the Eel River watershed.

It was completed in 1922 and began to fill Lake Pillsbury, which has a storage capacity of 74,993 acre⋅ft (92,503,000 m3) and releases water for the powerhouse throughout the year.

Some of the water from the generating station is used by the Potter Valley Irrigation District, while the remainder flows to Lake Mendocino.

[21] The East Fork Russian River is impounded near its mouth to form Lake Mendocino by the Coyote Dam, a rolled earth embankment built by the United States Army Corps of Engineers (USACE).

[24] A large amount of fine sediment is transported through the water diversion on Eel River, causing turbidity in Lake Mendocino during the first heavy runoff of the year and for several months afterwards.

The Coyote Dam impounds bedload, and the sediment-poor water it releases erodes the bed and banks of the river downstream in the Ukiah Valley.

[33] Numerous non-native species also inhabit the East Fork including bluegill (Lepomis macrochirus), brown bullhead (Ameiurus nebulosis), common carp (Cyprinus carpio), golden shiner (Notemigonus crysoleucas), green sunfish (Lepomis cyanellus), largemouth bass (Micropterus salmoides), redear sunfish (Lepomis microlophus), smallmouth bass (Micropterus dolomieu) and western mosquitofish (Gambusia affinis).

The rotenone poison was sprayed into the river, which had the effect of suffocating resident fish such as squawfish, suckers, roach, carp, hardhead minnows, green sunfish and lampreys, as well as smallmouth bass, and steelhead trout.

[35] A 2.6 mi (4.2 km) stretch of the river between Three Rocks Falls below Potter Valley down to Lake Mendocino is a class II+ run for kayakers.

The Three Rock Falls itself is a class V–VI rapid where several inner tubers have died, and should be avoided by most kayakers in most water conditions.