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Boat and PWC operators may encounter physical structures such as dams, locks, and bridges. You need to be extra cautious in these situations.

The Low-Head Dam

Dams pose dangers both above and below the dams.

The low-head dam is the most dangerous type of dam and has been named the "drowning machine." They may not be easily spotted because the top of a low-head dam can be several feet below the water's surface. Because of their small size and drop, low-head dams do not appear to be dangerous. However, water going over a low-head dam creates a strong recirculating current or backroller (sometimes referred to as the "boil") at the base of the dam. Even on small rivers, the force of the backroller can trap your vessel against the face of the dam and pull you under the water—even while wearing your personal flotation device (life jacket). Be aware that on large rivers or during high water the backroller or boil may be located more than 100 feet downstream of the dam. Avoid low-head dams.

Low-head dam

The Dangers of Low-Head Dams

Low-head dams pose a serious danger to vessel operators. Surface currents below low-head dams can suck vessels toward the face of the dam. Currents above low-head dams can sweep vessels over the dam. The recirculating currents and turbulent waters below these dams can swamp vessels and drown boaters.

The Large Structure Dam

Large-structure dams are more easily spotted because of their powerhouses and spillways. They can be dangerous to boaters and swimmers both below and above the dam. These areas are usually off-limits. Obey all warning signs and signals.

Non-lateral exclusion buoy