What visual indicator marks the eddy fence in swiftwater rescue?

The visual indicator that marks the eddy fence in swiftwater rescue is characterized by an obvious line in the water where the current moves in opposite directions. This line often appears when the fast-moving water of the river interacts with the slower-moving water of an eddy, creating a distinct and noticeable separation.

Understanding this line is crucial for rescuers because it signifies the boundary between the turbulent currents and the calmer water of the eddy. Recognizing this visual cue allows rescuers to identify safe zones where they can operate without being swept away by the stronger currents.

The other options represent different features of river dynamics but do not accurately describe the specific visual indicator of an eddy fence. For instance, the convergence of flow into a narrow channel can occur without forming a visible line, while a sudden drop in water depth signifies other geographic features rather than the dynamics of an eddy fence. A maintained glassy surface is indicative of calm water, which, although it can be found near an eddy, does not provide the necessary visual context to identify the boundary where the currents change direction.