A red buoy is floating at the harbor entrance.
lifebuoy; life ring
A ring-shaped or similar flotation device thrown to a person in the water to prevent drowning.
They threw a lifebuoy to the person who fell from the boat.
The lifeguard threw a life ring to the drowning person.
counter for small objects; counter for pieces · counter for military units · individual; one person · counter for years of age difference; counter for school years
Loanword from English 'buoy'.