Smack in the middle of Fredericksburg is a magical scene that plays out almost every evening in the summer: dozens of people splashing, swimming, fishing and wading in the Rappahannock River as it flows along the city's historic downtown waterfront, winding under car-choked bridges and busy train tracks.

As the sun begins to sink in the steamy Virginia sky, people gravitate toward the river, crossing soccer fields by foot, pulling their cars into spots along busy riverside roads or congregating at Falmouth Waterfront Park on the Stafford side of the Rappahannock across from downtown.

Falmouth has the area's only stretch of sandy beach, and it gets crowded come twilight. On the rocky Fredericksburg side, river visitors usually set up on outcroppings that jut from the bank's lush grasses. This time of year, the water is low -- usually 21/2 to 3 feet deep -- and waders venture out to sandbars or across the river, finding a cool respite from the heat and suburban bustle that increasingly describes the region.

"After work, I pick him up from day care, and we just cool off," said Anthony Perez, a pipe fitter, as he took a break on a rock with his 3-year-old son, Ethan -- both in water shoes. "It's beautiful and just comes up to my waist."

The two Perezes shared their rock with Shanna Amirez, her 9-month-old son, Charlon, and a purple plastic shark.

Amirez said that on many summer evenings she drives 30 to 40 minutes from her Orange County home just so she and the baby can splash in the Rappahannock.

"This is just a nice spot to, sort of, have for ourselves," she said.

The grassy banks and soft curves of the Rappahannock extend 184 miles from the Blue Ridge Mountains to the Chesapeake Bay. It's a communal river enjoyed by thousands of people for much more than its bucolic views. Some fishermen all but live off it -- eating the carp, bass and catfish they catch along its shores. Others attend church services along the river, where pastors wade in and baptize believers.

Smith Coleman was married alongside the river, at one of the campsites north of the city. An Orange County teacher who has fly-fished on the river since arriving as a freshman at what was then Mary Washington College in the 1980s (now Mary Washington University), Coleman said there is a "magical twilight" about the Rappahannock in the evening.

"Unless you are on it [in a boat] or wading in it, you can't quite imagine how pretty and aesthetic it is," he said. "You watch the light change, and you see a great blue heron doing what you're doing a hundred yards up. Then the peepers [frogs] come, and you hear all this amazing stuff, right in the midst of a really urban area."

But the lazy, peaceful scene of the Rappahannock can belie the river's danger. Although the river is no more than a few feet deep as it passes through Fredericksburg, its bottom has many holes, including some that plunge 9 feet deep. Since the 1970s, more than 70 people have drowned in the river, which can move deceptively fast and can overpower those who have drunk too much alcohol or don't know how to swim. Officials have recently begun posting large signs at popular swimming spots warning: "Danger! The river can kill!"

A disproportionate number of those who have drowned have been members of the Washington area's fast-growing Hispanic population, either locals or people who have driven down from Prince William County. Signs are now also posted in Spanish.

While public use of the river is one of the region's badges of pride, advocates recognize that the rising population around Fredericksburg -- now more than a quarter-million -- can easily endanger water quality and the health of fish and wildlife.

Since 1969, Fredericksburg, a city of 20,000, has owned 4,200 acres of riverfront property -- most of it in neighboring counties -- and there is virtually no riverside development for many miles. Compared with the neighboring Potomac, James and Shenandoah rivers, the Rappahannock has remained relatively protected and clean. But as the region's real estate values skyrocket, river advocates have been pushing much harder for the city to put the land in a permanent easement so no future city council could allow its development.

Bob Gramman, who has been canoeing the Rappahannock's whitewater sections since the 1970s, said he doesn't think the river has changed significantly, although he has. Now retired, he can take his boat out any time of day, and he loves being in the river well beyond sunset.

"We've done some beautiful moonlight paddles," he said. But how could he see? "It didn't matter. We know the river."

Another generation was coming to know the river one recent night along a short stretch of downtown boardwalk known as the City Dock. As an old-fashioned paddle-wheel tour boat churned south for a dinner cruise -- "The Love Boat" theme wafting from its decks -- Tammy Hawkins was putting a worm on a fish hook for her 10-year-old son, Devin.

"He just felt like fishing tonight," said Hawkins, who lives in Fredericksburg. "We're lucky we can just come down to the Rappahannock."

Ron Dumka plays with Charlie, left, and Lady on the bank of the Rappahannock River in Falmouth, which has the area's only stretch of sandy beach.