Which of the following is NOT a river hazard that paddlers should avoid?

Calm waters are considered a safe and ideal environment for paddlers, making them the correct choice for this question. Paddlers typically seek out calm waters for a more enjoyable and manageable experience, as these conditions are free from the dangers associated with river hazards.

In contrast, low-head dams, strainers, and rapids present various dangers that can lead to accidents and require caution. Low-head dams are particularly hazardous because they can create a hydraulic pattern that pulls objects underwater, posing a risk to paddlers. Strainers, which are obstacles like downed trees that allow water to flow through but can trap paddlers, can also be very dangerous if not navigated carefully. Rapids, characterized by fast-moving water and turbulent conditions, can be challenging for even experienced paddlers due to their swift currents and potential for capsize or collision.

Therefore, recognizing calm waters as a safe area, in contrast to the identified hazards, highlights why this was the correct answer.