THE SACRAMENTO RIVER SPILL: A CYCLE OF DEVASTATION

In California’s worst river disaster ever, the fishery in a 40-mile stretch of the upper Sacramento River to Lake Shasta was wiped out after a derailed tanker car spilled thousands of gallons of metam-sodium--a toxic weed-killer--last weekend. Experts predict it will take 10 years for the upper Sacramento River to completely recover from the catastrophe.

The area now endangered by the spill hosts a dramatic array of plants and wildlife, including the endangered California bald eagle and trophy-sized trout that lure fishermen from throughout the state.

In a worst-case scenario, the poison--which remains potent for up to 20 days--could work its way into the food chain. Among the possible effects:

* Biologists fear a possible disruption in the food source for the area’s mammals and birds.

* Fifteen percent of state’s bald eagle population resides in the region around Lake Siskiyou; the dead fish could prove lethal to birds that eat them.

* The large number of dead fish may continue to attract and endanger wildlife looking for easy meals.

At its highest concentration--97 milligrams per liter--the chemical destroyed almost everything in its path. (Only .07 milligrams per liter kills fish.)

Among the casualties so far:

* Algae on river rocks.

* Worms, insects and small organisms that form foundation of food chain.

* Brown and rainbow trout and other fish.

Known death toll:

* Tens of thousands of fish already suffocated by fumes.

Bushes and small trees along the river banks could be endangered; already there is evidence of wilting from the weed-killing chemical.

Without plant life:

* Fish will lose an important source of shade.

* Entire river channel could be destabilized through erosion.

* Insects will lose a key winter food source--the leaves that fall into the water and decay.

* Birds will lose nesting sites and shelter afforded by the bushes.

The chemical may target bigger animals that rely on the river for food or water

Among the endangered:

* Bears, deer, raccoons, minks, river otters.

* Bald eagles, fish-eating ducks called mergansers and other birds

Known death toll:

* At least one river otter, one bear and two deer. It is not known whether they died from noxious gases from the chemical or from contaminated water or fish.

REGENERATION OF THE RIVER

Biologists say the river eventually will recover, although it will take years. For now, officials will wait for the spill to dissipate on its own, by becoming diluted in the vast waters of Lake Shasta. The river could be artificially restocked with fish from hatcheries, but biologists discourage this move because outsider fish would have different characteristics from the natives.

THE PROCESS: Fish and the invertebrate organisms they feed on still survive upstream of the derailment and in a dozen major tributaries. In the coming months:

A) Currents will carry spores of algae downstream, allowing it to recolonize on rocks.

B) Adult aquatic insects on tributary streams will mate and lay eggs on the main river, beginning to regenerate.

C) Some fish upstream will migrate into the main river.

D) Rainbow trout, the most prized species, tend to stay in one area. Consequently, no significant populations will take hold until after the trout’s spawning season next spring.