The annual run of Northwest salmon from the vast Pacific Ocean to the mountain streams where their lives began- is one of Nature's most awe-inspiring events. To the Indians, who populated the Northwest first, returning salmon were an annual miracle.

Now that modern science has discovered some of the salmon's secrets, their journey seems even more miraculous.

So unlikely is the survival of a single returning salmon that Nature compensates heavily. Of the other 3,000 to 7,000 eggs in a nest, only one spawning pair, on average, will make it back. Too much or too little water at hatching can wipe out great swarms of young fish life. Bigger fish, bears, seals . . . all take their share of salmon. Nature allows for these natural events.

But Nature alone cannot make up for what people have done.

Dams blocked huge areas of the wild salmon's spawning grounds. Roads and towns sprouted up along rivers and streams. Logging and farming practices fouled rivers and creeks. So did pollution from the cities. And it became too easy to catch fish.

Salmon runs became smaller and smaller. Some types of salmon disappeared forever. Having nearly destroyed the salmon, people are now coming to their rescue. Still, important runs of Northwest native salmon are in real danger of extinction. Much remains to be done.

What follows here is a close look at the life of a single wild salmon. Oncorhynchus tshawystcha is her full biological name. We'll call this salmon Onco, for short. "Chinook" is another name people have given her. She also goes by "tyee" or "King salmon." By any name, Onco and her breed are the largest and most royal of all the Pacific Northwest salmon.

The Start of a Cycle

In late August, the leaves on streamside trees are yellowing. The smell of fall and colder weather is in the air, and morning frost collects on the bank. A reddish-brown female chinook idles under riffles of rushing water. She looks battered and exhausted. She's just waiting here, maybe resting.

A second salmon appears. He is darker than she is. Cream-colored splotches mark his body. He moves in beside her, upstream and parallel to her body. These salmon are spawning. The female chinook deposits about 5,000 bright pink eggs in the gravel bottom of her nest - called a redd. After the male fertilizes the eggs, the female moves upstream from her redd. With her tail, she kicks up pebbles that drift downstream to settle over the redd.

The eggs now are covered. They are protected from direct sunlight and strong current. For the next four weeks or so, the eggs are very fragile. The slightest bumping of the redd can destroy them.

By mid-autumn, the eggs begin to develop. Eyes begin to form. And somewhere among these closely-packed lives in the redd lies Onco. Onco the Lucky.

Onco is fortunate that the water temperature is only 55 degrees Fahrenheit. That's within a few degrees, up or down, of what her system can handle. She's lucky, too, that there is no sudden torrent of water in the creek. A heavy storm could dislodge the stream bed rock and crush her.

Upstream from Onco's redd, riffles mix air with water to give the eggs a rich oxygen supply. Without oxygen, the eggs would die.

Ducks and other birds hunt for salmon eggs. Raccoons find the same reward in shallow gravel. Adult trout, too, love salmon eggs if the trout can get to them. But they do not find Onco in the gravel-covered redd.

Aside from these natural hazards, the developing salmon egg has to survive some unnatural hazards.

In another creek like Onco's, a mining dredge once ripped up the stream bed. Now, each year the loose soil releases silt which spreads far downstream. Silt covers gravel and chokes off the oxygen supply in the water. The eggs suffocate. Grazing cattle can trample the stream banks, their muddy footprints releasing even more silt. Pesticides applied to upstream crops can drain into a creek and poison fish. A road built alongside a stream can change the way water runs off. The stream is more apt to flood after a big rain. Where once there were trees and shade, the sun hits the water directly. Direct sunlight can warm the water more than salmon eggs can stand.

Careless logging can ruin a salmon spawning stream. Branches and debris can block fish movements. Logs dragged along a slope, or a log truck crossing the smallest trickle, can churn up more silt. Of course logging removes trees and shade. Some of the worst damage was done before people quite understood how shade and plants are important to salmon.

Lucky for her, Onco's creek is in pretty good shape. For one reason, there are laws now that help protect salmon habitat- the natural environment salmon need to survive.

Dredge mining has been outlawed through most of the Northwest. Road-building codes are tighter.

In some places, logging is cleaner. People are working to protect streamside vegetation.

Things have changed. Many now realize that more wild salmon will become extinct if people don't back off and give them some room. We have to strike a balance between our needs and the needs of other living things.

Not that we can strike such a balance without paying for it. If it's tougher for a logger to get to logs, somebody ends up paying more for lumber. Outlaw dredge mining, and it costs more to get the minerals.

On the lower river, irrigators, power producers and bargers are changing the way they work - and having to charge more for their goods - to help protect wild salmon runs. Everybody must pay their share if Onco and her kind are to survive.

Sometimes it takes more than just backing off. People passed laws to rebuild some salmon streams that were destroyed by careless mining or logging. In some places, hatchery fish are being put back into streams where the wild salmon disappeared years ago.