"HEALING A River: 50 Years in the Life of the Potomac," a new exhibit at the National Museum of Natural History, is both more and less than its promising title implies.

On one hand, it's about a rare success story in the generally gloomy picture of progress in "saving" the waters of Chesapeake country, the bay and its many tributaries. The story is told to mark the 50th anniversary of the Interstate Commission on the Potomac River Basin, a governmental agency established "to give publicity to, and aid in" the river's cleanup.

This the commission does in a collection of nearly 100 color and black and white photographs arranged on panels with accompanying captions and text tracing the Potomac's progress from a sewage-filled tributary unsafe for human activity to a remarkably revived river.

A heightened public consciousness resulted in a crackdown on polluters and large expenditures of public funds to build advanced sewage treatment plants, the exhibit makes clear. There are also a few stuffed fish and waterfowl and a handful of live fish to illustrate the variety of wildlife.

But if the exhibit, housed in the North Gallery between the elevators and remains of ancient South American cultures, seems a bit scant, there is more to it than at first meets the eye. For the pictures also tell a tale of population growth and industrial decline.

And here is an irony: Industries that once polluted the river are no more, resulting in a cleaner Potomac but chronically depressed economies upstream. There is, for instance, a smokestack picture of the Celanese fiber plant near Cumberland, Md., now closed for almost a decade. A symbol of pollution downriver, it symbolized prosperity upriver.

The growth of the region from 1.7 million in 1940 to 4.6 million today -- a major factor in the pollution of the Potomac as sediment from subdivisions washed into the tributaries -- is well-illustrated. There is, for starters, a 1938 aerial photograph in which the fields appear much, much closer in. Local buffs will also have fun trying to identify the unidentified "new Arlington shopping center" with five-cent parking.

Then, there is a view of gridlock on the Memorial Bridge from Virginia in 1952. It cries out for alternate routes. But the growth since has merely moved the gridlock to newer highways and bridges intended to dissolve it.

Regardless, the Potomac is on the mend. If it is not yet the bountiful body of water first observed in 1608 by Capt. John Smith, nor is it the lifeless river symbolized in the sign that said: "Polluted Water. No Swimming or Wading."

The exhibit's most intriguing symbol, however, may be its image of "The Awakening," the Hains Point sculpture of a human form reaching out from the ground. In case you've ever wondered about the meaning of this unusual figure, the exhibit tells us that it "symbolizes the river's rebirth."

Unbeknownst perhaps to the exhibit's organizers, the statue is scheduled to be removed to make way for the Peace Garden -- another symbol which may or may not be more enduring.

HEALING A RIVER: 50 Years in the Life of the Potomac -- Through Jan. 25 at the National Museum of Natural History, 10th and Constitution NW. Open 10 to 5:30 daily. Metro: Federal Triangle.