At low tide on the Potomac River in recent days, Skip Shankle has guided his riverboat cruise around shoals and shallow spots that are new to him after 20 years on the river.

"The drought has totally changed the character of this river," said Shankle, captain of Capitol River Cruises, which takes tourists up the river.

Those who fish, kayak or canoe also have had to adjust to unusually shallow waters as the Washington area sweats through a severe drought.

Yesterday, nearly a week after about a billion gallons of water were released from the headwaters of the Potomac River to offset stresses on plants and wildlife from the drought, changes in water levels are nearly imperceptible, according to the Middle Atlantic River Forecast Center, part of the National Weather Service.

"This place has no oomph," said Hendrik van Oss, a researcher for the U.S. Geological Survey who was teaching a canoe class at Seneca Creek State Park near Potomac. "The place where we look for rapids is flat, so we're scouting around for new places."

Water from the reservoirs was released to maintain minimum water levels needed to protect life in the river, which now has 10 percent of the normal water flow for summer months. Without the added water, fish, plants and aquatic life would have been endangered, forecast center officials said.

Because the river is more shallow, the reserves flowing downstream from the Jennings Randolph Lake and Savage River Reservoir in western Maryland were slowed by friction with rocks along the river floor, according to the forecast center.

The last time the Potomac was this low, Twiggy was sporting miniskirts and race riots broke out in Chicago. That year, 1966, the river level actually dropped to about half of its current level.

"It's so low, the fish all go deep," said Chip Walsh, of Gambrills, who brought his 6-year-old son to a spot near Seneca Park yesterday to catch catfish and bass. "The fishing is really bad now. . . . We have to do things a little differently."

Walsh said he used to catch half a dozen fish in one outing to the shaded, slow-moving waters but would be lucky to snag any now.

Kayakers and canoeists also found changes. Quick-rushing danger spots, such as the Great Falls area, were more sedate, while generally placid places were too shallow and rocky to maneuver.

"The funny thing is, a half-foot can make a big difference," said Daniel Hellerstein, of Wheaton, trotting down to the river's shore near Old Angler's Inn with a kayak hoisted above his head. "It will be interesting to see what I find."

Some showed little worry about the changes, though. Paula Lambert, 49, of Largo, launched her kayak nearby with her stout Lakeland terrier in tow, swimming behind her on a leash as she braved the nearby rocky areas.

Lambert's dog, Phoebe, got sucked under a few times, she said.

"If . . . Phoebe can take it, I don't see why others can't deal," said Barbara Hoover, 45, one of Lambert's friends.

A shortfall of rain this year has created the drought conditions. There is no danger to drinking water supplies at this time, officials said, but some municipalities are encouraging voluntary conservation.

Owen E. Thompson, a meteorologist at the University of Maryland, said few cold fronts have dipped to the south since January to create conditions for rain and storms.

"You need that clash of cold and warm fronts to get the rain," Thompson said, "and we're just not getting that."