Eleven-year-old Reginald Harris, his eyelids droopy, sat quietly in the sun, fighting off seasickness. Tanya and Tumeka Brown, 13- and 11-year-old apple-cheeked sisters, pointed out with pride the sugar factory where their father works. Keith Rice and his pal Keith Timpson, both 11, ceremoniously lowered a black and white disk to test the murkiness of the brown water as the Osprey -- a 42-foot work boat outfitted with sampling and monitoring equipment -- took off for another day on the Chesapeake Bay.

A gaggle of girls, dubbed "The Water Quality Experts," crowded around a black box that measured the amount of salt in the water and its temperature. Mid-deck, another group of children gingerly placed a chemical in test tubes to measure the acid content of water pulled from the Chesapeake.

Such are the adventures aboard the Osprey, a floating classroom where each year 2,000 schoolchildren from the bay region learn firsthand about pollution problems in the Baltimore Harbor, one of the Chesapeake's most heavily industrialized areas.

The Osprey is one of 10 educational facilities from Havre De Grace, Md., to Hampton Roads, Va., run by the Chesapeake Bay Foundation, a private environmental group that since 1966 has been educating people about the frail and complex ecosystem of the country's largest bay. About 25,000 children attend programs at the centers each year, foundation officials said.

They said the idea behind the field trips is simple: recruit new generations who, after having their noses, eyes and pores exposed to the Chesapeake's pollution problems, will care enough about the bay to help make a difference in the future.

On a brilliant November morning recently, 20 sixth graders from Sarah M. Roach School Elementary School on Old Frederick Road in Baltimore piled onto the Osprey for a five-hour cruise.

The sixth graders' teacher for the day, "Captain" John Dugdale, a 24-year-old law school student and foundation employe, makes such trips six days a week to teach children from bay area schools how to test the troubled waters of the Chesapeake for the chemicals and biological conditions that are literally smothering life in the bay.

The Roach School contingent's adventure began with a slide show and combination history, science and urban studies class in a makeshift classroom aboard the Lightship Chesapeake moored at Pier 4 in Baltimore's Inner Harbor.

There, Dugdale tweaked the children's imagination with a plainspoken lecture about factory discharges, sewage, drainage from farmers' fields and city streets, acid rain and other pollution problems that threaten the Chesapeake.

Flashing a slide of what he described as "chocolate soup" mud, Dugdale warned, "There are 480 different kinds of poison in that mud. The mud isn't pretty, but the worst stuff you can't see."

Dugdale urged the children to do simple things to conserve water, such as not letting it run in the sink while they brush their teeth.

"Do you think your life is going to be ruined if you start saving water?" he challenged.

"No!," they yelled.

As the Osprey eased across the harbor, Tanya and Tumeka crimped their noses at the stench of tallow coming from a soap factory.

Latrice Coleman, 12, grabbed a clipboard and tackled the daylong task of checking off the names of cargo ships she spotted in the harbor.

While groups of children performed tests, others danced on deck to ward off the chilly wind. On the distant shore the small black cars on a coal dock chugged along like toy trains on tracks that rose 40 feet above the loading platform.

Children peered through binoculars for familiar sights.

"That's Fort McHenry, that's where Francis Scott Key first wrote 'The Star-Spangled Banner'!" shouted Tanya.

"That's tough!" chimed in 11-year-old Diron Williams.

Slowing the Osprey, Dugdale pointed to the Patapsco Sewage Treatment Plant and pulled some tiny "comb jellies" -- sewage-eating, jellyfish-like blobs -- from the thickened water.

"Why it smells kinda funky here is sewage," he told his charges.

"Ick!" they chorused. Tanya resolved to complain to Baltimore Mayor William Donald Schaefer.

English teacher Louise Zablocki, a 20-year veteran of the Baltimore schools, said the daylong cruises spark a new consciousness among the children.

"It's a beginning," she said. "When they go home, they'll do little things like not leave the water running when they're brushing their teeth. The little things, they understand those -- they're on their level."

The children are selected for the field trip for their interest, attentiveness and attendance records.

"They'll get a lot out of this; it gets them used to seeing what's around them in their own neighborhood," Zablocki said. "They see the harbor as a fun thing -- they don't realize the deepness of the bay in their own lives. And I think they're going to be conscious of it when they get older. They want it for their own children."

For Nola Cromer, the children's math and science teacher, the day on the bay is useful for a number of reasons. "No matter which group goes out, they want to take it further. This fits right in with a lot of the science programs dealing with plant life and animal life. And it helps Mrs. Zablocki with language if they write thank-you letters," Cromer said.

For lunch, the boats stopped at Tanyard Cove, a charming inlet off Marley Creek, away from the sewage plant and industries. From a perch on the shore, a big black and white osprey stared at its wooden namesake as the children ripped open brown bags stuffed with sandwiches, cookies and sodas.

Dugdale noted that pollution has touched even their serene picnic spot. The water is so tainted by sewage bacteria that Marley Creek has been closed to swimming and crabbing for six years, he said.

After lunch, his seasickness forgotten, Reginald raced to the back of the boat, where he volunteered to pull in a plankton net as a biology lesson unfolded.

Next, like a bucket brigade, the 20 giggling children formed a chain from stern to bow to help Dugdale pull aboard a 12-foot trawl net.

Squeals of delight greeted the catch, which included the blue plastic main stem of a "Big Wheels" bicycle and three "pinky-sized, see-through fish called bay anchovies -- two live and one dead.

To illustrate how fish filter oxygen through their gills, Dugdale pulled open the gaping mouth of the dead fish.

"Ouch!" groaned 20 empathetic mouths.

The two captives swam around furiously in a small plastic container as they were passed eagerly from hand to hand.

Linking the fishes' energy to an experiment performed earlier by the children, Dugdale explained that the oxygen level in the water that day, 9 parts of oxygen for every million parts of water, is healthy for all bay creatures.

Fish need at least 5 parts per million of oxygen to survive, he explained, while heartier creatures such as crabs and eels can survive with only three parts per million.

As the Osprey headed home for the Inner Harbor, the children talked about what they planned to do differently in their lives to save the bay.

"I'm going to report the people who are littering in the bay to the police," vowed 11-year-old Melvin Coates. "And I'm going to try not throw things in the bay," he added.

"It's fun and educational, learning about how the water's being polluted . . . " chirped Dineen Bethune, an outgoing 12-year-old. "When I'm washing the dishes . . . I'm not going to leave the water running anymore. And I'm going to tell my parents and my 8-year-old sister."

"If I see anyone polluting the water when I'm on my uncle's boat, I'm going to tell them to stop," said 12-year-old Christine Eckles.

For 11-year-old Gregory Bellos, the lessons seemed somewhat more cosmic.

"I learned about the salt in the bay and about how the companies and the industries pollute the water. And I learned about the osprey bird," he said.

"But most of all, I decided I'm just not going to fight anymore with her brother," said Gregory, pointing at Christine. "He gets me real mad -- last week he threw ice water on my little brother -- but I'm not going to fight anymore."