Shark Trouble by Peter Benchley

caprices. Some people harbor the belief that they can out-muscle the ocean. No one can. And yet there are some who will die trying.
    Here are some basic lessons I’ve learned and some simple precautions to take that will help keep you and your children from getting into trouble while swimming off a beach. They require nothing more than a rudimentary knowledge of how oceans work, the patience to study the water you’re about to enter, and a healthy dollop of common sense.
    Ocean Water Is Always Moving
    It’s a fact you must take on faith: no matter how calm the surface may appear, the water beneath is never still. It is moving in three dimensions: back and forth along the shore, in and out from the beach, and up and down to a degree dependent on the slope of the shelf of the beach.
    Water is driven constantly by wind, tides, and currents, and by local phenomena like channels, jetties, and points of land. The presence (or absence) of reefs, shoals, and sandbars will alter water’s motion; prevailing winds will drive surf onto certain beaches and leave others to be lapped by little but the tides.
    If you intend to swim in the ocean on a given day, it makes sense to stand for a moment and study what the water is doing that day. The wind will be pushing waves onto the beach, and since winds rarely blow directly
at
a beach, the waves will strike the shore at an angle, causing a current called a “set” or a “drift” that moves the water in a particular direction.
    Look at swimmers already in the water or at pieces of wood or seaweed floating on the surface, and note which way they’re moving and how fast. That will tell you how strong the drift is and how quickly you’ll be carried away from the point where you enter the water. The stronger the drift, the closer you should stay to shore and the more carefully you should plan where you want to exit the water, because here is another inexorable fact of ocean swimming:
    You Cannot Swim Against a Strong Current
    If you try, you will exhaust yourself and probably precipitate a chain of events that may lead to disaster: fatigue, gasping, breathing water, choking, panic, struggling for air, waving or calling for help, sinking, and, finally, drowning.
    If you want to emerge from the water near your blanket, your Yoo-hoo, and your can of Pringles, walk up the beach in the opposite direction of the drift, enter the water, and let yourself float down the beach until you reach your exit point. Then swim gently
across
the drift toward shore. Otherwise, be prepared to float away from your home base and walk back when you’re finished swimming.
    Under
no
circumstances should you try to swim against the current—the only exception being for swimmers with a lot of experience in the ocean and a dedication to vigorous exercise. For years I swam a mile a day for exercise, and when I was at the shore, I’d calculate the drift with the intent of swimming as hard as I could against it while managing to stay in place. I was always alert, though, for the onset of fatigue, and when I saw myself slipping away from a fixed point on the shore, I’d immediately swim across the drift and get out of the water.
    There are a few naturally occurring phenomena that can sometimes (but not always) be seen from the shore, that can be deadly but don’t have to be, and that you can anticipate—just by being aware of them—whether or not you see them coming.
    Undertow
    This is a term that is universally known and widely misunderstood. Many people use
undertow
to mean
any
action of waves, currents, or tides that can jeopardize their safety. In fact, undertow is a very specific phenomenon that occurs mostly on narrow beaches with steep scarps, or drop-offs. It is, simply, the action of water thrown ashore by a wave returning whence it came.
    After a wave breaks, gravity will carry the water back to sea. If the drop-off into the sea is steep, the water will