What hazards may be encountered on downriver trips?

The correct choice is low-head dams and strainers, as these are significant hazards that can be encountered during downriver trips, particularly in areas with flowing water, such as rivers and streams.

Low-head dams present a serious danger because water flowing over these structures creates a hydraulic condition that can trap and drown paddlers or boaters, often before they even realize the danger is present. Strainers, which are obstacles like fallen trees or branches that allow water to flow through but can catch objects or people, can also pose a serious risk as they can easily ensnare paddlers and make it difficult to escape.

Awareness and avoidance of these hazards are crucial for safe navigation while paddling or boating in downstream environments. In comparison, the other hazards mentioned, such as high tides and coastal currents or underwater caves and whirlpools, are more relevant to different types of water environments, such as oceans or deep lakes, rather than typical downriver scenarios. Similarly, fog and strong winds can affect visibility and navigation but are less specific hazards associated with downriver travel compared to the immediate dangers posed by low-head dams and strainers. Understanding these specific threats helps ensure a safer experience when engaging with river environments.