Which of the following conditions would best be defined as "reduced visibility"?

The most appropriate condition that defines "reduced visibility" is fog, rain, or mist. These weather phenomena create obstacles to clear sight, significantly hindering a boater's ability to see other vessels, navigation markers, and potential hazards on the water. When visibility is reduced due to fog or rain, it becomes crucial for boaters to employ additional precautions, such as using navigation lights and sounding their horn, to ensure safety on the water.

Bright sunny weather, on the other hand, typically provides optimal visibility, allowing boaters to see clearly. Clear skies at night can also present challenges for visibility, especially without sufficient artificial light, but they are not as commonly associated with reduced visibility as fog or rain. Windy conditions alone do not necessarily impede visibility; they may affect the water's surface and how boats handle, but visibility remains unchanged unless accompanied by precipitation or fog. Therefore, choosing fog, rain, or mist aligns directly with the definition of reduced visibility.