The "miracle" of the Monongahela has been undone.

The river, which flows 128 miles from the mining-scarred mountains of West Virginia to the coal-fed steel mills of Pittsburgh, had been one of the most polluted bodies of water in the United States.

However, the Monongahela was reborn two years ago. Strict clean-water laws, affecting industry and coal mining, turned a dead river into a flourishing sport-fishing stream and a recreational asset.

Residents along the winding shores, ecstatic at the turn of events, dubbed the river the "Amazing Mon." The Environmental Protection Agency included Monongahela on its list of "success stories," joining other once-polluted rivers such as the Willamett in Oregon, the Detroit in Michigan, the Buffalo in western Tennessee and the Escambia in Florida.

But in late January, the Monongahela was dealt a potentially lethal blow. No one knows if it can come back one more time.

For a six-week period, and possiby longer, massive amounts of acid West Virginia have poured into the tributaries of the Monongahela. The river, normally able to neutralize an occasional discharge of acid, has been socked with too much for too long.

At least 14 miles - and perhaps more - have been destroyed. The affected area runs from a point one mile north of the West Virginia-Pennsylvania line to a point two miles south of Brownsville, Pa. From there, tributaries of the north-flowing Monongahela have diluted much of the acid.

Fish by the hundreds have been killed. Water treatment plants are struggling to make river water potable. Towns along the Monongahela that had planned to celebrate in July the rebirth of the river now are wondering if those festivities would be a farce.

It's too early to assess the damage. Scientific studies cannot be conducted until summer when the weather improves.

But first reports are discouraging. More than 120 pounds of dead carp - the heartiest fish in the river - have been counted.

"When you kill a carp - God almighty, you can throw a carp up on the bank and leave it for a day and come back the next day and throw it in, it'll swim away," said Jim Yadamec, an avid fisherman and outdoor columnist for the Uniontown, Pa., Morning Herald.

As a result of the acid spill, conservationists believe it will take a "a minimum" of seven years for the food chain to revive sufficiently to support fish once again.

"We really don't know what we've got left to save or how to go about it," says Roland W. Schrecongost, of EPA's Wheeling, W.Va., field office. "It's scary and awful sad."

There are a lot of people saying the same thing up and down the river.

"This is one of those success stories - you get right up to a peak and then something like this happens and knocks the skids right out from under it," says Jim Ansell, who oversees part of the Monongahela as a waterways patrolman for the Pennsylvania Fish Commission in Fayette County.

Late in January, acid wastes began pouring into two streams that feed the Monongahela, the Tygart and Cheat rivers. The cause is unknown; the source is unknown; the solution: do nothing.

"Right now, this thing pretty much has to run its course. There's nothing else we can do," says Denzil Courtney of the West Virginia Department of natural Resources.

"No one knows how long something like this will continue," says EPA's Schrecongost. "It could be several weeks or a matter of months."

An irony is that such massive acid spills are a "fact of life" and may have occurred here frequently in the past. However, because the river was so dirty before, no one paid attention to them.

The coal in the hills is high in sulfur, as is the rock surrounding the seams. Water that collects in the mines combines with the sulfur to become sulfuric acid.

Under recent mining laws in Pennsylvania and West Virginia, waste water from active mines must be treated to remove sulfuric acid and other pollutants. But active mines are far outnumbered by the thousands of abandoned mines that honeycomb the hills.

No laws cover them - at least not in West Virginia. Pennsylvania voters in 1968 enacted a $150 million bond issue to finance clean-up of abandoned mines.

Mine drainage has become a critical problem. Each rain or thaw, which alters the subterranean water table, could bring a whole wave of acid groundwater into the watershed.

That may be what happened to the Monongahela this time. West Virginia officials now think so. Others blame it on the coal strike and an intentional dumping of acid by mine owners.

But a check of active mines in West Virginia indicated that all waste-water treatment plants were operating, despite the strike.

As acid continues to pour into the Monongahela state conservation officials wait and watch. It is a difficult task for Courtney who once fished the "new" Mon.

"I work on this during the day and grieve at night," he said.