What is surrounded by water and gives warning to sailors of dangerous rocks?

This fortunately, led them away from the dangerous rocks.

It is apparently private, surrounded by dangerous rocks and shoals.

The main takeoff is close to a dangerous rock which often sticks out of the water, and has caused injuries.

With any luck, the offshore breeze would keep the ship away from the dangerous rocks.

The Napoli dodged the last dangerous rock, and shot forward into open water.

Next morning they found themselves in a dangerous rock studded sea with a small island upon their starboard quarter.

Some of the islands were surrounded by dangerous half-submerged rocks.

This helped soften his image as a dangerous rock 'n' roller.

Hope it's not rocks under the surface or anythin' dangerous.