Buoy

A floating shape anchored to the bottom to mark out a channel; also floated over a shoal, or near a rock, as a warning to mariners. The following names distinguish the various styles of buoys in use: Can, Spar, Bell, Nun, Cask, and Whistling, which are defined under their respective headings. (See Beacon.)

A buoy is said to watch when it floats upon the water over its anchor.

To stream a buoy is to drop it into the water before the anchor leaves the cat head.