MENDOCINO CO., 5/27/26 — For 104 years, the rainbow trout in the cold tributaries above Scott Dam have carried a secret they could not use. Pearse and Kannry’s genetic work, summarized in Friends of the Eel River’s 2025 comments to the state water board, shows the resident fish still hold much of the code for a sea-run life: the chemistry to slip downstream as smolts, turn silver, run to sea and come back heavier as summer steelhead, the southernmost ghost of Northern California’s runs. Two concrete plugs have kept that code from being tested. Once those plugs are removed, the trout can live out their code to run to the sea.
That is the smallest, strangest fact in the Potter Valley Project’s dismantling. Two rivers will live different lives once the dams come down. The Eel, bled for more than a century through a 9,257-foot tunnel under the divide, starts to regain itself; the Russian, drinking imported Eel water since 1908, learns to live thinner. The critters on both rivers are about to get the news.
This tour runs from the bare bottom of what used to be Lake Pillsbury down to the harbor seal haul-outs at Jenner: eight stations across two watersheds. Some critters win, some lose, and most will have to learn a different river.
Station 1 — the drained reservoir
Scott Dam holds back the upper Eel into Lake Pillsbury, a 2,300-acre reservoir completed in 1922. Under PG&E’s surrender and decommissioning plan, removal could begin as early as 2028. The lake bottom will be exposed, and what lived in the lake mostly does not live in the river.
Largemouth bass, bluegill and crappie, the warm-water fishery that draws Bay Area weekenders, are gone from this place, or reduced to whatever side ponds managers maintain elsewhere. None of those fish are native to the Eel. They were put there because there was a lake.
The bald eagles and ospreys that nest around Pillsbury lose a grocery store. Eagles can adjust; ospreys have a harder time of it. Neither species will disappear from the stretch, but the reservoir buffet does. In time, a returning salmon run could feed them on a different schedule.
The tule elk lose open water but not the valley-bottom forage. The exposed bed won’t become paradise overnight; it will pass through mud, weeds and raw ground first. But willow, cottonwood, sedges and meadow plants are the long game, and elk know how to use a river bottom.
The pikeminnow may be the loss nobody is grieving. Sacramento pikeminnow were introduced to the Eel in 1979, supposedly through an illegal bucket-stocking into Pillsbury, and from that warm slack water, they spread through the basin to become one of the most damaging nonnatives in the system, a major predator on juvenile salmonids across the mainstem and South Fork. Pat Higgins’ Eel River Recovery Project has documented their spread for more than a decade.
Pikeminnow thrive in the kind of water dams make: slow, warm, simplified. Take the slack water away, and the cool, fast post-removal river is, finally, the wrong river for them. They won’t vanish overnight and may not vanish at all, but the Eel’s most notorious nonnative finally will lose ground.
Station 2 — the 12 miles between the dams
From Scott Dam down to Cape Horn Dam is about 12 river miles of canyon, hemmed by the Mendocino National Forest. For a century this stretch has been a controlled river: flow set by upstream releases, sediment held back by the same dam.
The first years of removal will be hard on the river. Studies estimate Lake Pillsbury has accumulated roughly 21 million cubic yards of sediment, with about 12 million potentially available for downstream transport, and however the work is staged, those years bring turbidity, burial and a moving bed where a reservoir held the river still.
Aquatic insects get hit first. Caddisfly larvae build stone cases on cobble, so bury the cobble in silt and the caddis go with it. Mayflies and stoneflies take the same hit, and any remaining native freshwater mussel beds are vulnerable to burial too. The lower Eel has survived great sediment violence before, including the 1955 and 1964 floods, but survival was never easy.
This is also where Pacific lamprey begin a quieter return. The larvae are wormlike, blind and ancient; they burrow into fine sediment and filter for years before they run to sea, and when the first pulse passes and the new bed sorts itself, some of that new sand becomes the material they need.
Tribal restoration programs call lamprey a forgotten keystone. The adults carry ocean nutrients deep into the basin, and their bodies feed everything from black bears to belted kingfishers. Lamprey were here when these mountains were rising, and they are about to have a much larger upper basin to work with again.
The foothill yellow-legged frog lays eggs on cobble bars in spring as flows drop, and a dam that releases cold or high water late can drown or chill the clutches. The post-removal pattern of natural snowmelt and rain recession through May and June is closer to what this frog evolved with. The first year is rough on the frog; after that, spring runs closer to the rhythm it evolved with.
Station 3 — Cape Horn to Outlet Creek, the dewatered decades
Below the Cape Horn diversion, the upper mainstem Eel has been running a half-river for generations. In recent decades, roughly 60,000 acre-feet a year has been pulled through the tunnel into the East Fork Russian, and in dry summers the reach from Cape Horn down past Hearst to the Outlet Creek confluence at Dos Rios has run nearly bone-dry, what remained warming past salmonid comfort and sometimes past survival. Native Fish Society’s 2015-16 monitoring clocked the mainstem at 78 degrees Fahrenheit at Bloody Rock Roughs, above what juvenile steelhead can ride out for long.
Dam removal won’t give salmon cooler or fuller summer water, which is the common expectation. Lake Pillsbury catches winter rain and releases it slowly through the dry months, so when the lake is gone, the summer release goes with it. The pre-1922 Eel ran low and warm by August on its own, and that is the river the salmonids evolved with. What dam removal restores is passage and timing, not August volume.
In the first years after removal, the upper mainstem may even run drier in late summer than it did with managed Pillsbury releases, which makes the cool tributary refuges — Tomki Creek, Outlet Creek above Dos Rios, cold springs and shaded side channels — more important, not less. Juvenile steelhead and Chinook will hold in those refuges through the worst stretches.
What’s new is that they can move. The Cape Horn fish ladder, 434 feet long with 49 pools, was never enough. Van Arsdale’s counting station logged 9,528 steelhead in 1944-45. By recent years the count had fallen to the single thousands, some years to near zero. With the dam gone, the ladder no longer matters, and the counting station, which has been on this river since 1933, will close.
Above the former Scott Dam site, the upper mainstem opens to sea-run fish for the first time since the early 1920s. River otters get a whole reach to work: they key on lamprey, suckers and salmonid juveniles, and all three prey bases should change as passage returns. American mink follow the same edges. Belted kingfisher and American dipper, both tied to live streams, gain water that behaves more like a stream, and common merganser, which times broods to fry emergence, gets a different nursery.
Of all the upper-basin returns, the summer steelhead matters most. Charlie Schneider, CalTrout’s connectivity program manager, has put it plainly in public interviews: the wild trout already up there show where fish want to be, and the door just has to open. Pearse and Kannry’s genetic work suggests the door is real, and the first wild summer-run adult to swim past the former Scott Dam site will be the loudest critter event in the modern Eel.
Station 4 — mainstem Eel, South Fork to Pacific
Below Dos Rios the Eel takes in the South Fork and runs to the sea at Centerville. The sediment pulse follows months to years later, through the lower river, estuary and nearshore ocean. Muddied water at the mouth is a real cost for a year or two.
Once the pulse passes, the lower river gets something it has been denied for a century: a natural sediment and wood supply from the upper basin. Rivers build bars, riffles, floodplains and estuaries with the material mountains give them. A century of trapped gravel, sand, wood and organic matter cannot be released without harm, but the river also needs that material to heal.
The half-pounder steelhead, the Eel’s signature subadult, returns to fresh water after one rather than two saltwater years. It gets better passage and a river stitched more closely to its own seasonal cues. Fall Chinook gain upper-basin habitat in numbers; a 2024 run estimate cited in California Sportfishing Protection Alliance field reporting put more than 18,000 adult Chinook in the watershed that year, a reminder that the river is constrained, not dead.
Green sturgeon are a slower story. The Eel has nearly lost them, and their recovery runs in human generations. Dam removal is not primarily a sturgeon project, but a healthier estuary, restored sediment process and stronger salmonid runs can only help the lower-river food web they belong to.
At the mouth of the Eel, the Wiyot Tribe and restoration partners have been working the Ocean Ranch Unit and the Eel estuary, where young salmon fatten before the ocean and returning adults gather before the run upstream. The estuary has been scoured, diked, drained and simplified by a century of damage, and it now gets a real chance to work as an estuary again. Federally endangered Tidewater goby belongs in this story, as do juvenile salmon, steelhead, longfin smelt and the invertebrate soup that feeds them.
Harbor seals at the mouth depend on more than fish; the sediment supply that builds and reshapes the beach also shapes their haul-outs. Shorebirds on the mudflats are mostly on the edge of this story, with sea-level rise their bigger concern.
Station 5 — the disconnect
On the Russian side of the divide, the 9,257-foot tunnel that has carried Eel water under the ridge since 1908 will no longer run year-round. The 2025 Water Diversion Agreement transfers PG&E’s diversion right to the Round Valley Indian Tribes and authorizes a smaller run-of-river facility near the old Cape Horn site, to be built and operated by the new Eel-Russian Project Authority. PG&E wants it built during dam removal, not after, so the East Branch Russian goes less time without Eel water.
The new facility does not replace the old project. It would divert only under seasonal rules and Eel flow floors. In wet periods some water still crosses the divide, but in dry summers, when the old diversion mattered most for downstream agriculture, storage and recreation, the Russian River should expect little or no Eel subsidy.
The wildlife on both sides of the divide are facing different futures. On the Eel side, the river regains passage, sediment and natural process. On the Russian side, the system loses a summer cushion that has quietly underwritten it for three human lifetimes.
Station 6 — Lake Mendocino and the East Fork Russian
Lake Mendocino is not coming down. The late-1950s Coyote Valley Dam is a separate U.S. Army Corps of Engineers structure, not part of the Potter Valley Project. But its inflows drop sharply when a run-of-river facility replaces year-round plumbing—less water means less water stored and less flexibility to release in summer.
The lake’s own ecology is reservoir ecology: smallmouth bass, bluegill, crappie. Lower lake levels mean less reservoir habitat in dry years, and the ospreys nesting around the lake, the bald eagles wintering on it, and the white pelicans and double-crested cormorants working the surface all see less working water in dry periods. None of these are at-risk species, and the lake will still be a lake, just a smaller, thinner one in the years when water matters most.
Summer baseflow on the East Fork below the dam — and on the mainstem Russian below Hopland, where the East and West forks meet — depends on releases from Lake Mendocino. Those releases are shrinking: recent state flow orders have set lower minimums. Sonoma Water, the regional water agency, and Russian Riverkeeper, the watchdog group, are publicly at odds over how to manage the watershed. Riverkeeper wants earlier water-use cuts to protect the lake’s carryover storage and cold-water pool.
Station 7 — Russian mainstem, Ukiah to Wohler
The Russian carries two sea-run populations listed under the Endangered Species Act: Central California Coast steelhead and Central California Coast coho. Steelhead spawn across the basin; coho hang on in cooler tributary refuges such as Mill Creek above Healdsburg, Dry Creek below Warm Springs Dam, Green Valley, Mark West and the shaded side water where summer still gives them a chance.
These populations have been holding on inside a flow regime that included a steady Eel subsidy through the East Fork all summer, and taking much of that subsidy away brings the concern into focus around juvenile rearing from July through October. Juveniles need cool water, cover, food and depth enough to hide, and lower flows can mean shallower, warmer, more fragmented habitat and more concentrated predator pressure from nonnative bass.
The flow number alone doesn’t tell you what the fish are dealing with. Federal regulators have cut summer minimum flows on the Russian so cold water stays banked in Lake Mendocino for release later, when fish need it most. Where the cold water sits, when it gets released and which area it cools matter as much as the gross volume.
The foothill yellow-legged frog faces different conditions on the two rivers. On the Eel, removing the dam restores the natural spring drop in flows that the frog evolved to spawn with. On the Russian, the picture is mixed: less imported Eel water means shallower summer flows in some stretches, hurting tadpoles, while changed release patterns may help in others.Western pond turtle, California’s native freshwater turtle, basks on log jams and rock outcrops along the Russian. It tolerates a wide range of flows but needs pools deep enough to overwinter and connected water to move, so fewer deep pools in dry years would be bad turtle news, slowly rather than dramatically.
North American beaver have been quietly recolonizing the lower Russian and its tributaries. They are flow-tolerant by trade, building their own pools, but a thinner mainstem makes that work harder and pushes the action toward tributaries and side channels with enough gradient, wood and water to hold a dam.
River otters do roughly the same thing on both rivers: they make a living wherever fish, crayfish and cover remain. The urban edges from Ukiah down through Healdsburg suit them better than people expect, and they may be the one species that comes through this transition about even.
Station 8 — the estuary at Jenner
The Russian does not run to the Pacific in a straightforward way. It hits a sandbar at Jenner that closes in summer when wave energy exceeds the river’s outflow, opens when the river rises, and functions as a lagoon when closed. Sonoma Water has spent years writing and revising the management plan for this estuary, balancing flood risk to Jenner homes against juvenile steelhead and coho habitat, harbor seal pupping and the haul-outs on and near Penny Island.
Under a thinner-flow regime the bar can close earlier and stay closed longer, and by itself that can be good for lagoon-rearing fish; the lagoon becomes a warm, productive, food-rich nursery for juvenile steelhead and coho, fattening them before they smolt. A closed lagoon that stays brackish and oxygenated raises young salmonids well. The same lagoon, if it gets too warm or too cut off from tidal exchange, can kill them. Water quality decides which it becomes.
For harbor seals, the picture is mixed. Seals pup on the river bar and nearby beaches from spring into summer, and a stable closed bar can be good pupping habitat, while a sudden mechanical breach during pupping season is not. Lower flows tighten the management trade-offs because flood risk, fish habitat and seal disturbance all have to be balanced on a smaller water budget.
Tidewater goby is important in some North Coast bar-built lagoons, including the Eel estuary and nearby Salmon Creek, but there’s no current survey confirming it at Jenner. The lower Russian’s reliable estuary fish are jacksmelt, surfperch, starry flounder and other natives that respond to water quality, salinity and food.
The estuary’s birds track those fish: great blue heron, snowy egret, belted kingfisher, osprey, double-crested cormorant, the wintering common loon and red-throated loon, the brown pelican in fall. The shorebirds on Goat Rock Beach, the sanderling and killdeer and willet and marbled godwit, care less about the river than about the ocean and the beach. They stay mostly on the edge of this story, watching the rest of the critters sort out a smaller river.
What the ledger says
Step back from the eight stations, and the picture isn’t symmetrical.
One of the clearest winners is Pacific lamprey, which regains access to a much larger upper Eel. The Eel’s summer-steelhead life history, reduced to a remnant possibility for a century, gets its first real chance in 100 years, and fall Chinook gain habitat in numbers. A 2020 peer-reviewed modeling by Cooper et al. projects between roughly 1,000 and 10,000 returning adult Chinook above the former Scott Dam site, a wide range that points toward recovery either way.
The clearest loss is the Pillsbury reservoir community: the bass and bluegill, the lake-edge foraging patterns, the human summer lake culture, which ceases to exist as a habitat type. It is a loss even if the fish themselves are not native to the Eel.
Between those two clear cases, the picture is harder, and most of the difficulty is downstream of the ridge. The lower Russian River, cut off from more than a century of imported Eel water, runs thinner in summer. Its steelhead and coho juveniles, its frogs, turtles, pool fish and aquatic mammals were already under pressure, and the pressure just got worse. Sonoma Water and Russian Riverkeeper will spend years politely arguing over flow and demand. The critters don’t get to weigh in on the modeling.
The Eel goes back toward being itself. The Russian learns to be smaller. The plumbing that connected them for more than a century comes apart, and the two rivers, which were never really one river even when the tunnel ran year-round, finish the slow uncoupling that began when the old two-basin compromise stopped being financially or safely sound.
The lamprey won’t know anything happened. The summer steelhead, if it returns, will know only that the door is open. The Pillsbury bass will be gone. The seal pup born at Jenner, on a bar that closes earlier than it used to, will live a slightly different summer.
Two rivers, two futures, and a lot of critters working it out.