Buoy:

Navigational aid. There are several types and colors of buoys of which the most numerous are: the black can (seen as a fuzzy black spot on the horizon); the red nun (seen as a fuzzy black spot on the horizon); the red or green day beacon (seen as a fuzzy black spot on the horizon); and the vertically striped black-and-white channel marker (seen as a fuzzy black spot on the horizon).