Low-head dam

A low-head dam is a man-made wall that runs all the way across a river or stream, with a drop of anywhere from six inches to 25 feet, according to the U.S. Army Corps of Engineers (opens in a new tab). They look harmless, but they are among the most dangerous places on a river.

The danger is below the wall. Water pouring over the dam can form a recirculating current, sometimes called a hydraulic, that pushes people and objects underwater and spins them around, making escape almost impossible. The National Weather Service (opens in a new tab) describes it as an upstream-directed current that is extremely difficult to escape. Nearly 800 deaths have been recorded at low-head dams in the U.S., according to the Corps.

What to know:

• they are not always visible from upstream or downstream, so learn where they are before you paddle or fish;
• stay away from both the upstream and downstream sides;
• when in doubt, get out and scout, as the Corps advises;
• never try to rescue someone caught below one by going in; call 911.

April is Low Head Dam Public Safety Awareness Month. See low-head dams and river safety.

What you can do today: check the map of any river you plan to paddle for dams and plan where you will get out.