Which action is most crucial when navigating through fog?

When navigating through fog, reducing speed is the most crucial action. Fog significantly reduces visibility, which can make it difficult to see other vessels, obstacles, or navigational markers. By slowing down, a boater has more time to react to unexpected situations and can navigate more safely through potentially hazardous conditions. Reduced speed allows for better control of the vessel, ensuring that the operator can stop quickly or maneuver effectively if needed.

Other actions, like using a loud horn or attempting to increase visibility through various means, are also important but are secondary to the fundamental need for speed control. While verifying your location can be helpful, if you're moving at a high speed during low visibility, you risk collisions with other vessels or objects, regardless of whether your position is accurate. Thus, the primary focus in foggy conditions should always be on reducing speed to maintain safety.