Dams, Locks, and Bridges and Changing Water Levels
Boat and PWC operators may encounter physical structures such as dams, locks, and bridges. You need to be extra cautious in these situations.
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." 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.
Locks safely transport boats from one water level to another, like an elevator. When approaching a lock, remember that commercial traffic always has priority over recreational boats. Enter the lock only after you've been signaled to enter by the lock's traffic lights or by the lock attendant.
Most states have laws requiring that you pass under bridges at a slow speed. You should always reduce your speed and proceed with caution near any bridge or man-made structure that decreases visibility and passage.
Fluctuating water levels can cause special hazards for boaters. Water levels can change rapidly due to tides, flooding rivers, or water released through dams. Any of these conditions can cause boats to run aground in areas where navigation may have been safe earlier.