From a distance, Charles Thomas' farm along the Monocacy River looks like an olive green canvas that an intemperate artist has spattered with tiny bursts of red, white, blue, yellow and pink.

The pinpoints of color are waterlilies, which poke above the surface of ponds covering 50 acres of marshy bottomland. They signal to visitors making their way along the winding, back roads of Frederick County that Lilypons Water Gardens, the Bloomingdale's of aquatic gardening, is at hand.

"Until the last 25 years or so aquatic gardening was really thought of as a rich man's endeavor," said Thomas. "Today, most landscapers wouldn't consider a garden complete unless it contained a water feature."

Cultivating aquatic plants in garden ponds is one of the fastest-growing trends in gardening, said Mark Cathey, director of the National Arboretum. Thousands of homeowners have spent from $255 to $2,000 or more to build or have ponds installed in their yards, he said.

Lilypons is the largest of four companies nationwide that specialize in aquatic plants, exotic goldfish, and all the hardware needed to build a pond. And, according to Thomas, the farm here in the shadow of Sugar Loaf Mountain has sales of more than $2 million a year.

Dark pools filled with fragrant waterlilies and languid fish have been symbols of serenity and bliss, not to mention royalty, since the days of the Eygptian pharaohs.

But there is practical side to their popularity as well, Thomas quickly adds.

"For one, you don't have to water the plants, and there are no weeds," he said. "In fact, the water gardeners who do the least are the most successful."

Before the turn of the century, ponds were found in only the most exquisite formal gardens. But by the 1920s, they had been discovered by the noveau rich. Suddenly there was a demand for lilies, goldfish and all the accoutrements of aquatic gardening, he said.

Thomas' grandfather, George Leicester Thomas, a Frederick farmer and real estate developer, also fancied the flowers. He grew waterlilies and bred goldfish as a hobby in a roadside pool. So many people stopped to inquire if they were for sale, he decided to go into business in 1917. The family has been in waterlilies ever since.

Business was so good, Thomas said, that U.S. postal authorities agreed in 1936 to open a post office at the farm to handle the volumes of correspondence generated by the company's mail-order business.

Leicester Thomas decided to name the post office and his waterlily enterprise after Lily Pons, then a world-acclaimed opera soprano. The rural lane on which the farm fronts also was renamed Lilypons Road.

Pons was so thrilled by the honor she traveled from New York that year to participate in the dedication of the business and the post office.

Thomas said his father, George L. Thomas Jr., wrote what is considered to be the definitive book on water gardening. Three of Thomas' four daughters, who range in age from 19 to 23, also work at the farm.

Last year, Thomas, who has written two books on water gardening, helped found the Water-Lily Society, which has a worldwide network of members. His wife, Sally, won a national award for the design of the company's catalog.

The 265-acre farm, set in southern Frederick County about six miles west of I-270 and about 25 miles north of Washington, has 400 flower and fish ponds, spread over 190 acres.

The ponds, used to propagate plants and three types of ornamental fish, are filled with water fed by gravity through a system of pipes and canals from Bennett Creek, a Monocacy tributary.

About 200 types of aquatic plants and 100 varieties of waterlilies are grown at the farm. Customers have come from throughout the United States and also buy through the company's mail-order catalog, Thomas said. Waterlilies, the most popular seller, range in price from $17 to $75 a plant, depending on the degree of difficulty in propagating them.

The company also specializes in lotus blossoms and holds an annual lotus blossom festival in July. The flowers normally bloom no earlier than July 9; but this year, because of consistently warm weather, the first flowers appeared in June.

Lotus blossoms sell in the same price range as waterlilies, but certain tropical bog plants, such as iris, can cost up to $175 each.

For years, the biggest stumbling block to creating a water garden was building a pond, Thomas said. Until the 1960s, concrete was the only building material widely available.

But since then, fiber glass pools and pools with plastic liners have become the industry standard, and prices have dropped dramatically.

A 6- by 4-foot plastic-lined pool with a pump and filter and a stock of plants and fish costs $355, Thomas said. A fiber glass pool alone costs that much, while a concrete pool alone would cost as much as $1,000, he said.

Ornamental fish prices start at $3 a pair. But Imperial Japanese carp, also known as koi, can sell for up to $225 a pair, depending on their size. Fish can also be purchased in quantities of up to 100 or in breeding collections.

"Goldfish are just about the easiest, most inexpensive pets to take care of that you can have," said Thomas. "They can even be trained."

Clapping one's hands or ringing a bell before feeding can produce a Pavlovian response in fish, prompting them to swim to the surface at a certain spot on command.

"Where I lived as a child we had a big brick lily pond, and I just loved it," said Mary Orzech, a Reston, Va., resident who was browsing at the farm last week. "Someone gave me five goldfish, so now I think I may have another one."

"They're just nice to look at," added Kim Moulton, whose husband, Glen, built a pond at their Calvert County house two summers ago.

"In fact, we're building a new house on five acres and we're definitely going to have another," she said.