What's Weightless, Visible To The Naked Eye, And When You Put It In A Barrel Of Water It Will Make The Barrel Lighter In Weight?

Riddle: What's weightless, visible to the naked eye, and when you put it in a barrel of water it will make the barrel lighter in weight?

Answer: A hole!

Source: https://www.riddles.com/1205

Riddle: What's weightless, visible to the naked eye, and when you put it in a barrel of water it will make the barrel lighter in weight? Answer: A hole! — by Anonymous v1.

Riddle: What's weightless, visible to the naked eye, and when you put it in a barrel of water it will make the barrel lighter in weight? Answer: A hole! — by Anonymous v2.