A visitor must accept water lilies on their own terms.

That means arriving at Kenilworth Aquatic Gardens, where lilies and lotuses float in a score of small ponds, in early morning or late evening. In the middle of the day, perhaps the most convenient time to plan an excursion, the blooms close in the hot summer sun.

It also helps to see Kenilworth on naturalist Walter MacDowney's terms.

"Look," he ordered some visitors one morning, pointing across a lily pond. There, almost completely hidden by hibicus, a green heron extended its neck to the sky as ten silent, astonished humans watched from ten feet away. He stretched slowly, and then snap! His beak opened and closed and he folded up toward earth.

MacDowney looked at the bird in amazement. "Well," he finally said, "A group of birdwatchers were out here last week and spent all morning looking in vain for a sight like that."

MacDowney, who grew up across the street from the gardens in Northeast Washington, can answer questions about almost every leaf and insect on the 11 acres next to the Anacostia River.

During a 90-minute nature walk he conducts, he manages to talk about edible wildflowers, local folklore, bees, snakes and bird calls. Oh, Yes -- and about water lilies.

True, if you go yourself, you'll see dragonflies and frogs resting on lily pads and snakes winding their bodies around the long stems. You can amble by small ponds and crouch along the edges so you almost fall in.

But you'll miss learning the origin of the marshmallow, the location of laden honeycomb and the story of a Manchurian lotus germinated from seeds that are a thousand years old.

Kenilworth was once the property of W.B. Show, a Civil War veteran who planted a few water lilies on his riverside property in 1882. By the time he died, he'd quit the government job which originally brought him to Washington from his home in Maine. He raised flowers full time.

Now Kenilworth is part of the National Park Service and a staff of eight coax the lilies from tuber, or walnut-shaped fleshy root, to a flower whose peak blooming season is early August.

In winter the staff cares for the tubers of the tropical lilies, which are planted in greenhouses in water troughs. Tropicals are replanted in ponds every year; hardies, as their name suggests, remain in the ponds even when ice covers the surface.

During the summer, ranger Freddie Lundy and his staff skim the surface of the lily ponds and the greenhouse troughs to remove a solid mass of little green dots called duckweed. They weed out some of the other aquatic plants which, if left to multiply, would strangle the delicate lily plants. They dredge the ponds of the silt and muck from the Anacostia River water flowing in through a network of pipes.

It's a job without end.

Lundy started working at Kenilworth 30 years ago. He came to Washington to work in "some big government building." He found a government job all right. It wasn't precisely what he expected.

"I sure had problems with the snakes at first," he laughed. "How did I know I would come to Washington and have a job where I had to deal with snakes?"

Lundy estimates it took him seven years to get to the point where he felt knowledgeable about water lilies. He still isn't too wild about snakes.

"A few old-timers used to visit here a lot and give me their advice," said Lundy. "Now I get people who'll come when they have a question for me, like what kind of lily they should buy for their backyard." CAPTION: Picture, no caption, By Margaret Thomas