WASHINGTON — Summer on the Potomac River too often comes hand in hand with tragedy.

As humidity peaks and temperatures soar, better judgement yields to the temporary desire for comfort. And an ankle-deep wade into the seemingly docile waters can quickly become a fight for survival.

Already this year a swimmer, 21-year-old Marco Reyes-Sanchez, surrendered to the river’s invisible hand. His body has yet to be found but he is presumed dead.

Police are also trying to identify the body of a man pulled from the water Sunday afternoon.

“Last year we ran 118 calls…no drownings,” says Captain Andy Bell with the Montgomery County Swift Water Rescue Team. “Most of those calls were in the Billy Goat Trail area, injured people from falls or on the rocks, or climbers on the rocks.”

In those situations it is easier and faster for Bell’s team to reach the scene because the trail runs right against the river, he says. That access also creates danger, as the river beckons in the middle of a hot hike.

“The Potomac especially is very deceptive, it has some spots that look very calm, very tranquil, look very easy to swim in,” he says.

“But, because the river is a very high-volume flowing river there is a very strong undercurrent with lots of rocks, lots of unseen obstacles and the water is never clear, so you can never see what you’re getting into.”

These dynamics are especially pronounced in the area of the river called the Potomac Gorge. It is a turbulent zone where water comes into conflict with geology. This stutter-step in the earth’s crust makes Great Falls a beautiful spot, it also makes it dangerous.

But, the falls are only a piece of a complicated section of river spanning about seven miles. Uprooted trees, chaotically strewn boulders and the detritus of civilization upstream create a gauntlet so dangerous for swimming, that merely getting in the water is illegal.

“The river is moving fast and there are a lot of hazards that you can get pinned up against, get your feet trapped in,” says Bell. “And the trees, they create what we call a strainer effect where, if you get swept into them, you can very easily get caught and trapped by your body.”

Even wading into the river can lead to a dangerous situation. Mud and silt and pollutants make it impossible to see more than a few inches below the water’s surface. The river’s bottom is too often taken as an article of faith. And Bell says that faith is easily misplaced.

“I feel like I’m safe because I have my footing and I step into an eddy or something and I’m relatively safe there, but then as soon as I take one step to the rear of where I’m at it’ll drop from a four to five foot to a 20 to 30 foot drop. And as soon as you lose that, you run that panic sensation and you can very easily drown.”

Bell and his team are well-trained, with plenty of experience. Even so, he says it’s tough to rescue someone once they are already in the river’s grasp.

“Usually we’re out of the fire house within a matter of a minute, and then we have to go down there and it’s going to be five to ten minutes to get to the river’s edge to put the boat in. And then it’s going to depend on where in the river from where we launch as to how long it takes us.”

Given all that, Bell says it can take up to 20 minutes just to reach the scene.

“They could very much be in a fight for their life prior to us arriving, and have lost that fight.”

Signs of recreation dot the riverscape just before a section called the Breaks. An ill-advised rope swing dangles just feet above a bubbling section of stream. Floating docks outfitted with barbecue grills and second story platforms sit within an errant slice of the Trump National Golf Club. Canoes and kayaks and rowboats sit parked under trees rooted in the river’s bank. The river should be enjoyed, but not at the expense of respect.

“It creates a false sense of security, and it lures you into the sensation that you can get your self out of trouble,” says Bell.

Too often, though, by the time swimmers realize they are in trouble, it’s too late.

WNEW D.C. Bureau Chief Kris Ankarlo contributed to this report. Follow him and WNEW on Twitter.