A ridge of rock or sand at the surface of the water is called a shoal.

Here's a breakdown:

* Shoal: A shallow area of water where the seabed rises to within a short distance of the surface, often creating a hazard to navigation.

* Sandbar: A ridge of sand deposited by waves and currents, typically found near the shore.

* Rock outcrop: A visible area of bedrock that rises above the seafloor.

While all of these terms describe submerged elevations, "shoal" is the most general term that can encompass both sandbars and rock outcrops.