Pacific salmon come from a long lineage. The oldest species known by fossil, Eosalmo driftwoodensis, lived fifty million years ago, while Oregon was still tectonically assembling itself. The most dramatice family member to date was Smilodonicthys rastrosus, a lunker species that has caused many sport fisherman to investigate time travel. This fish, which swam our waters five or six million years ago, was ten feet long, weighed five hundred pounds, and was equipped with long fangs--the saber-toothed tiger of salmonids.

Salmon as we know them probably evolved in the course of the last two million years. By one theory, they derive from freshwater fish that took to sea out of Pleistocene necessity, displaced by glaciers from their native lakes and rivers. Others argue that their anadromous habit is much older, but at some point in evolutionary time, salmonids acquired the capacity to survive in both salt and fresh water and to orient themselves on epic North Pacific travels. It still isn't known how they navigate at sea. Sensitivity to the sun or stars seems unlikely. It may be, some researchers believe, that salmon are somehow attuned to Earth's magnetic field, following pathways of extremely low-voltage current that eventually return them to the mouths of their native river systems. Close to shore and in fresh water they probably proceed by means of sensitivity to temperature changes and direction of flow, but mainly by an exquisite sense of smell capable of discerning the unique chemical signature of their home waters.

The Pleistocene glaciers left a desolate landscape of gravels and bare basalt. As grasses and shrubs and trees gradually dispersed from unglaciated refugia, salmon pioneered the reopened waterways, adapting to the nuances of individual drainages, fertilizing the gravels with spawn and their spawned-out bodies. Willows and other riparian vegetation slowly took hold, stabilizing banks and bars. Millenia passed, salmon thronging the rivers in enormous runs that interblended throughout the year. Eventually conifers stood near streams again, their shade moderating water temperatures as the climate warmed, their toppled trunks restraining the erosive power of floods, trapping gravels, forming pools and riffles. Young salmon came of age in the structured streams, gaining strength for their journey by feeding on the carcasses of the old. Raccoons and bears and eagles came for the carcasses, dispersing the rich captured life of the North Pacific deep into woods and mountains. Old-growth forests and mountain meadows are transmutations of the bones and flesh of countless salmon.

A forest or meadow ecosystem, any ecosystem, is a complex abundance tuned toward its own persistence. The system does not immunize its member species and individuals against disaster, but it does weave its lifeways into a many-stranded resilience capable of absorbing disaster and easing its harshest blows. Fire in a healthy prairie or forest is normally not a catastrophe but an agent of renewal, a destroying creator, and floods in a healthy watershed are the same kind of force. They flush sediment downstream and onto the floodplain, where it fertilizes vegetation. They claim new driftwood and rearrange wood already in the river, forming new pools and deepening exisisting ones, reinvigorating their food webs. And spring flood surges carry millions of juvenile salmon, called smolt, hundreds of miles to the sea--the smolt, with little strength yet, face upstream, relying solely on the current to get them where they need to go.

The specific means by which floods renew stream ecosystems are still largely unknown. Researchers discover them piecemeal, one at a time, through dedication and good luck. A recent study involved the October caddis, a large orange insect relished by adult steelhead. (The steelhead is a large anadromous form of trout; a trout is a salmon that stayed in the river). In the spring, caddis larvae graze periphyton like sheep in a pasture. Smaller species of insects get little to eat and fare poorly, and young steelhead, who rely on those small insects (the caddis is too big for them, and too well armored in its case of silk and pebbles) also do poorly. They grow slowly. But if there comes a winter flood of sufficient magnitude to roll sizable rocks in its bedload, those rocks will smash a great many October caddis cases while doing less damage to smaller insects, which find refuge in cracks and depressions. In the spring the smaller insects will get a greater share of periphyton forage, young steelhead will get more to eat and fatten faster, and the steelhead species--along with steelhead fishermen, among other scavengers and predators--will have been well served by the violence of rushing water.

The dams we humans build are intended to restrain that violence, and they mainly succeed, to our benefit. But they also mute or eliminate altogether the ecological benefits of floods, and a hundred and fifty years of accumulating economic activity has dramatically amplified the damage floods do. The draining and conversion of wetlands for agriculture has forfeited the absorptive value of those natural sponges and laid their soil open to erosion. Building roads along rivers and hardening their channels with levees and dikes merely exports the power of floods downstream. In the watersheds of the Cascades and Coast Range, clearcuts and logging roads have increased peak stream flows by 20 to 30 percent. A clearcut slope releases ten times the sediment a forested slope will; the hemorrhage declines over time but does not fully heal for thirty years. Logging roads are even more damaging, boosting the chance of landslides by ten to a hundredfold. Logging road mileage in Oregon national forests has more than tripled since 1960. The total now stands at over seventy-three thousand miles.

Erosion in mountain watersheds is naturally periodic, most of it taking place in concentrated bursts during major deluges. In watersheds riddled with roads and clearcuts, as virtually all of ours are, those epochal storms can cause wildly cascading destruction. Two hours of the benchmark flood of 1964 produced twice as much erosion as would occur in the next thirty years combined. The flood of February 1996, though lesser than the 1964 event, will likely tell a similar story when studies are completed, and future floods will repeat the tale. Huge river and stream flows are nothing unusual in Oregon. In the flood of 1861, the Willamette River's discharge at Albany was measured at nearly triple the 1996 peak level. A current ran four feet deep through downtown Salem. Every mill in Oregon City was swept away. In 1907 there were three floods in a single year, two of them bigger than 1996. Since 1860 there have been some fourteen Oregon floods of the 1996 magnitude or greater, an average of one per decade.

Salmon evolved with floods and by means of floods. Like volcanism and the great ice flows, high water has never daunted them for long, but in this eye blink of evolutionary time we call human they face grave troubles. A century of logging has suffocated their spawning gravels with silt and raised the crucial water temperatures of formerly shaded streams. A century and a half of ranching and farming has denuded and broken down stream banks, turning cold deep flows into warm shallows, and laced stream waters with harmful fertilizers. Riverside industries have exposed salmon to chemical effluents that nothing in their evolutionary past has prepared them for. Dams on the Columbia kill nine out of ten smolt on their migratory journey; dams on the Snake, Deschutes, Klamath, and Middle Fork of the Willamette have walled salmon away from major portions of their ancestral habitat. Hatchery fish crowd out the wild populations, spread diseases among them, and dilute their finely tuned genetic heritage through hybridization. Wild salmon still return to their birth waters, but in ragtag remnants of their former runs. The waters no longer support them. The home they made in the Pleistocene is falling apart.

John Daniel is the author of six books of poetry, essays, and memoirs. A two-time winner of the Oregon Book Award for Literary Nonfiction, he lives not far from the Long Tom River in the Coast Range foothills west of Eugene. "Swimming Among the Ruins" was first published in Oregon Rivers.

To order a copy of OREGON SALMON: Essays on the State of the Fish at the Turn of the Millennium (from which this essay is excerpted) call (503) 222-9091 or email info@ortrout.org