The river runs through US

It's the tributary to America's heart.

From its start in Pittsburgh, Pa., at the confluence with the Allegheny and Monongahela, to where it empties into the Mississippi in Cairo, Ill., the Ohio River makes up 10 percent of the nation's navigable waterways - and 40 percent of its river traffic. Endless coal barges feed the 49 power plants on its banks, supplying electricity to much of the Southeastern and Midwestern United States. Large-scale corn and soybean growers flank the river and irrigate with its water. Roughly 3 million Americans drink it.

Sixty years ago, the Ohio was so glutted with hops, coal ash, pig innards, steel waste, and chemical poisons that it actually stank. Today, the river faces subtler - though perhaps no less serious - threats: runoff from cattle farms and agricultural areas, overflows of raw sewage, and the invasion of an insidious new species.

This summer, a group of scientists from four local colleges set out to navigate the river's 981 miles, to test the scope of its problems and consider how - even whether - it can survive the challenges threatening many of the nation's waterways.

"This is no small thing," says microbiologist Miriam Kannan, readying one of the team's two boats for Day 5 of the 10-day expedition. "We are this river. It's a circle: from poop to drink and back again, the river runs through us."

Lewis and Clark rode this river, and thousands of "river rats" followed them west along its treacherous course, seeking their fortunes in flat-bottomed shanty-boats and patched-up skiffs. Before them, the Shawnee and Ojibwe fished its shallows and trapped along its banks. The Ohio spoke to all these, and on down the generations: to Mark Twain, to William Least Heat Moon, to so many others that by now it should be hoarse.

When we put in at tiny California, Ky., the river is running high with new rain. The Monark, the team's 18-foot research vessel (shaped like a bathtub toy, flying bright college pennants), chugs through water that looks like diner coffee with extra cream.

Apart from the global positioning satellite hookup, the sonar depth-finder, and a device called a datasonde that tests water chemistry, the scientific gear on board is surprisingly low-tech. Students Lisa Smith and Dave Harris scoop up river water in Mason jars and record their bearings in photocopied log books. Prof. Mike Miller catalogues water filters in squares of marker-scrawled aluminum foil. Formaldehyde, to preserve mussels and algae, travels in a neon-green sippy cup.

"We still have to spend a lot of time in the lab, especially in the winter," says Ms. Smith, a senior at West Virginia's Marshall University who plans to pursue her master's in environmental microbiology. "But to me this is the real science, the science of being out there in the world."

As the Monark makes its way downriver toward Cincinnati, the team's larger pontoon boat is covering the 50 miles of river north of California. Both boats stop every five miles to sample the water; scientists on board are gathering data for 20 different experiments on three main environmental problems. Their findings will help the US Geological Survey (USGS), the Environmental Protection Agency (EPA), and other monitoring bodies develop a better understanding - and new regulations for the care - of what French explorers once called la belle rivière.

The Monark's first stop is a floating dock on the Kentucky bank that looks as though it has seen its share of floods. Lisa and Dave don life vests and hop into the muddy water to scour the dock's underside for an exotic species of mussel.

Natives of Norway, zebra mussels first came to the Great Lakes in 1989, probably in the bilge water of a boat. Since then, the voracious super-breeders have populated almost all the major inland waterways in the eastern half of the US. As they spread, they've been killing off already-threatened native mussels - the canaries in the underwater coal mine - says aquatic biologist John Hageman.

They've also been causing other changes. Because mussels eat by filtering water, the thousands of invading zebras that scientists found on last year's River Run had made the water much clearer.

Though that sounds like a good thing, it causes problems for the Ohio. For one thing, the aggressive filtering stirs up old poisons like PCBs and dioxin locked in the sedimentary layers of the river bottom. These toxic chemicals work their way up the food chain until they're dangerously concentrated in the carp and drum fish that have adapted to feed on the zebras.

Also, cleaner water means more light penetration and algae growth. That could be healthy in moderation, but the explosive growth is now having disastrous consequences downstream in the Gulf of Mexico, where the huge algal blooms end up and eventually die. Bacteria rush to decompose them, sucking all the oxygen out of the water, and creating a "dead zone" in which nothing else can live.

Dave and Lisa find about 30 zebras clinging to the dock: not as many as last year, but more than the team found in the flood two years ago. After taking water and algae samples, the boat gets under way.

At the back of the craft, aquatic ecologist Mike Miller is hand-pumping water through a series of filters, one to strain out larger algae, or phytoplankton, another to catch bacteria and river-bottom clay. These he'll send to the USGS and the EPA, which will use the data to decide how to regulate chemical dumping. But Dr. Miller, of the University of Cincinnati, is most concerned about nutrients: nitrogen- and phosphorus-rich fertilizers that wash off farmland and feed river algae instead.

"It's like someone turned on a huge spigot of corn syrup," he explains, squinting distractedly at a low-flying plane. "This river is the biggest contributor of nitrogen and phosphorus to the Gulf," and as the algae grow fat on these nutrients, so does the dead zone, an area thought to measure between 20,000 and 50,000 square miles at its summer peak.

Suddenly, Miller leaps to his feet. "You know who that is?" he shouts to the others, waving his River Run cap over his head, "I just realized: It's the US EPA! They're here because of us."

In fact, they're here because of a chance call Miller made a week ago to a former student who now works for the EPA. When he told her about the project, she got excited - and got the bureaucratic wheels turning with unheard-of speed.

Now the EPA is following the scientists, using a super-sensing device called a hydrospectral scanner to gather data - about the clarity of the water and the presence of oil spills and exotic toxins in the river - to coordinate with theirs. Miller says the government hopes to refine the flying scanner so that it can be used to detect concentrations of toxins that might indicate terrorist activity.

"This is really coordinated science here," he says. "We've got the USGS on board, the US EPA. I've never seen anything like this."

Then again, he says, "we're doing something nobody ever does: a snapshot of a whole river in essentially a day."

The Monark travels from a quiet stretch of river into an industrial area and on into downtown Cincinnati, whose shoreline is a cascade of cement steps. Leaving the city, the boat passes a major sewage treatment plant. It's one of the main concerns of the trip for Smith and her microbiology professor, Charles Somerville. The two are studying the presence of E. coli-related bacteria and antibiotic-resistant bacteria in the water due to fecal matter - both human (20 antiquated sewer systems around Cincinnati overflow into the river when it rains) and animal (cow, pig, and other droppings wash off nearby farms).

These animals, Smith explains, are increasingly plumped on antibiotic-enhanced feed, which makes them grow faster, but also makes them resistant to antibiotic treatment if they do get sick. And resistant bacteria are good proselytizers, says Dr. Kannan, of Northern Kentucky University. Three in a large intestine can quickly convert the rest, resulting in medically untreatable infections. Fast-food giant McDonalds made headlines last month by announcing it will phase out its use of antibiotic-fed beef, pork, and chicken by the end of 2004. Sweden recently banned antibiotic use for all but sick animals.

If a large intestine is fertile ground, a river contains an infinite number of potential bacterial converts. That's what worries Dr. Somerville. "Now some strains of antibiotics are almost useless," he says. Running out of antibiotics before new types can be discovered or manufactured has become a serious concern. Somerville's study is testing for resistant strains of commonly prescribed medicines: cipro, or ciprofloxacin, the best known anthrax treatment; tetracycline, often used to treat pneumonia, acne, and bladder infections; and erythromycin, employed for respiratory infections and syphilis.

"We were going to do vancomycin" - a "last resort" drug doctors prescribe for infections that resist every other treatment, Smith says. "But a bunch of the guys in our lab are like, 'We don't want to know if there's anything that's resistant to vancomycin.' " Bacteria resistant to all known antibiotics could potentially be used as biological weapons.

At the end of a long day, the Monark crew is met at Aurora, Ind., by one of the trip's organizers, Dr. Hageman of Kentucky's Thomas More College. They load the craft onto its trailer, then make for the lab, where they'll prepare test specimens in petri dishes before they break for dinner. Tomorrow they'll be off again, for another 100 miles of la belle rivière.

"No one else is doing this," says Somerville, "and it's so important." The Ohio River basin cuts through America's heartland, he says, so studying the river "is like taking your pulse: You get to know what's happening in your whole body by looking at that one spot."