It's a sign of the season that no one wants to see: rescue workers combing area rivers and reservoirs for swimmers missing in water that appeared as calm and enticing as a swimming pool.
After four drownings in Baltimore County this week -- all of them in deceptively placid areas where swimming is prohibited -- local authorities and safety experts are warning the public to obey the posted signs.
A calm surface, they say, can hide rocks, unstable ledges and underwater cliffs, along with currents made swifter by torrential rains. Caught off-guard, weak swimmers can struggle for survival, sometimes in remote areas with no lifeguards nearby and where a cell phone is of little use for friends trying to summon help.
"Reservoirs and lakes are very deceiving because of their tranquillity," said Robert Ogoreuc, an assistant professor of physical education at Slippery Rock University in Pennsylvania and a training officer for the Ocean City, N.J., Beach Patrol. "I call it the old swimming hole syndrome. It's inviting. There are no waves. You want to get in and cool off. What could go wrong?"
That can be a formula for tragedy -- just a foot or two from shore, unwary waders can find the bottom dropping off into a reservoir as deep as a 12-story building. "They end up panicking, and that's when they get in trouble," Ogoreuc said.
Or they disregard the warnings along a stretch of river below a dam, only to be grabbed by the swirling currents underneath.
Maryland's Vital Statistics Administration recorded 47 accidental drownings in 2004 and 51 in 2005. At least a dozen people have drowned so far this year -- and that number is sure to increase through the summer, officials warn.
On Monday, 16-year-old Ryan McCurley of Halethorpe drowned in the Avalon area of the Patapsco Valley State Park below Bloede's Dam, in an area where authorities say swimming is prohibited.
The incident is similar to one in June last year in the same area, when 28-year-old Pedro Peralta of Baltimore was sucked under the dam after deciding to wade in and cool off while picnicking and fishing.
"The other day, a park person came by and told us not to go by the dam, but she said that tubing was OK," said Colleen Boland, 19, of Catonsville, who swam in the Patapsco yesterday about 100 yards south of the roaring structure. "My dad told me not to tube today because of all of the rains. So we don't go out any farther than about 4 feet deep, because then it drops off."
Some incidents, including several this year, took place in areas that are off limits.
On Thursday, Adam Klank and Justin Smith, both in their early 20s, from Shrewsbury, Pa., died after Smith swam across Prettyboy Reservoir, saw Klank struggling and jumped back in to rescue him. Both men went under a few minutes later. Their bodies were recovered there.
On Sunday night, Keith Alan Cannon of Edgewood slipped off of a ledge at the Loch Raven Reservoir. The 17-year-old could not swim.
Reservoirs can be tempting. Often, nothing in the water appears to be moving; beneath the surface, however, currents of a river, several streams or runoff from the watershed all flow into the bowl and toward the dam at the reservoir's lower end.
Depth is another reason why swimming is prohibited in Baltimore County's reservoirs and the three managed by the Washington Suburban Sanitary Commission. The largest of the sanitary commission's reservoirs, Rocky Gorge, is 120 feet deep.
"Signs are posted, and we have a 14-officer police force," said Lydia Wilson, a spokeswoman for the commission. "We've never allowed swimming. It's just too deep."
And even relatively shallow water can be hazardous.
Ricky Ricketts, 51, is a fisherman who visits Prettyboy Reservoir dozens of times each year. He said he recently saw a young man dive in the water there -- only to come up injured seconds later.
"His leg was cut," said Ricketts, a Dover, Pa., resident who was at the reservoir yesterday. "It's very easy to get tangled in the water with the submerged rocks that are 10 to 12 feet under. ... And when you're diving, it's very easy to reach that depth."
Riverbeds below dams can also be unpredictable. Yesterday, some parts of the Patapsco River were swollen, and currents roiled along the river's top. But in other areas, sandbars seemed to halt the river's flow entirely. The water would just reach an adult's ankle.
At Bloede's Dam yesterday, the only visible "No Swimming" sign was painted on the dam with a white background and black letters. The sign, which is difficult to spot, instructs people to call 911 in an emergency.
But as McCurley's family discovered Monday, cell phones do not work at bottom of the valley. Rescue crews found McCurley's body about an hour after his mother first screamed for help -- and after other park visitors rushed out to where they could make a call.