The three most dangerous days of the year in the outdoors arrive this weekend.

Nine months of pent-up energy -- work or school, and for many, just plain not having enough fun for a long time -- will be unleashed in a 72-hour span over Memorial Day weekend.

When people bust loose after being held down, they can be drawn to high-risk behavior. Like a young adult floating down a cold, high river in an inner tube without a life jacket, with a six-pack roped alongside to be consumed along the way.

Few look in the mirror and say, “Today I will risk death.” Yet on Memorial Day weekend, thousands risk catastrophe with nary a thought. Don’t increase that risk by driving impaired by alcohol. And in most cases on the water, wear a life jacket.

For the start of summer, many will venture out on a powerboat, sailboat, kayak, raft, dingy, pram, inner tube -- that is, anything that floats. Sooner or later, you’ll end up in the drink.

Problem is, gravity wins. If you find yourself in the water with no easy way to extract yourself, you will eventually get tired, sink and end up in the vicinity of Davy Jones’s Locker. Unless, that is, you wear a life jacket. Then you can usually keep your head above water long enough to get pulled out.

On a hot sunny day on a boat, few like wearing life jackets, especially youngsters on inner tubes, suntan-seekers, fishermen in bass boats, and all who drink a lot of beer.

One answer is the new generation of unobtrusive inflatable life vests. You hardly know you’re wearing one. Buy ’em; wear ’em. You only get one chance at this event called life, you know.

Some have learned their lessons and wear a life jacket. Many have not, do not. According to the U.S. Coast Guard, 758 people died in 686 fatal boating accidents in 2011. Seventy percent of those boating-accident fatalities drowned, and of those, 84 percent were not reported as wearing a life jacket.

The laws are explicit: All children younger than 13, every person on a personal watercraft and every person being towed, must wear a life jacket. A life jacket must be on board for every person. That’s pretty simple. Yet people don’t do it.

Rivers often provide a worst-case scenario on Memorial Day weekend for young adults. When you take a tumble into a cold river, the “gasp-reflex effect” can hit you. Your chest feels tight, it’s hard to breathe and all your strength and mental clarity disappears. Pro rafting outfitters require all aboard to wear the best life jackets and wet suits and have a great safety record. Because of the cost factor, do-it-yourself kids on a raft often choose otherwise.

Contact Tom Stienstra at tstienstra(at)sfchronicle.com.