The National Park Service is firing up for its annual battle against boaters, sunbathers and rock climbers who violate its bans along the Potomac despite the number of lives lost in the river each year.

At Great Falls National Park, the rangers are increasing their foot patrols along the shoreline and will distribute new flyers that warn of strong undertows and powerful currents. While the river can look deceptively gentle, the eight-mile stretch from Great Falls to Chain Bridge has seen 30 accidental drownings since 1980, including five last year.

"You have current that is extremely strong, massive undertows, and the river in this particular area is deep and swift," said Stephen Pittleman, a park ranger at Great Falls.

Downstream from Great Falls, the Army Corps of Engineers has just completed $3.4 million worth of modifications to the Brookmont Dam, which has been known as "the drowning machine" because of its ability to trap anything that enters its spill.

Although the Corps of Engineers has eliminated the dam's deadly recirculating hydraulics by placing bags of concrete at the foot of the downstream side, engineers warn that it is still dangerous, even potentially life-threatening.

There are still "Danger -- Deadly Undertow" signs near the Maryland shore, and buoys with warning signs 2,000-feet upstream from Brookmont. "It's recommended that nobody get near it," said Harold Kanarek, a Corps of Engineers spokesman.

New this year, too, are Maryland regulations that prohibit boating 100 yards upstream of the Brookmont Dam or 200 yards above the Washington Aqueduct Dam near Great Falls National Park.

These regulations took effect March 10, and violators will be fined $30, according to Lou Ritter, a police sergeant with the Maryland Department of Natural Resources.

Violators who enter the river illegally from national parks on either the Maryland or Virginia side also can be fined up to $500 for a first offense, authorities say.

For the river's rangers and police, the headaches always begin about this time of year, when winter cabin fever drives crowds into the sunshine -- and to the rocks.

Last weekend, roughly 10,000 people visited Great Falls National Park, bringing coolers and radios, college books and swimsuits. They were seen hopping along the cliffs, sometimes with apparent disregard for the dangers below.

The accidents often involve carelessness, and sometimes alcohol or drugs. Most victims are 15 to 25 years old, Pittleman said.

Dangers are even greater now, he added. The rocks are still covered with slippery silt from last fall's floods, and the 40- to 45-degree water temperature can mean risking hypothermia -- subnormal body temperature -- within three to five minutes.