The ocean is a huge body of water that is constantly in motion. General patterns of ocean flow are called currents. Sometimes theses currents can pinch off sections and create circular currents of water called an eddy. You may have seen an eddy if you've ever gone canoeing and you see a small whirlpool of water while you paddle through the water.

An eddy is a section of circular current that tends to flow in the opposite direction from the main river current. Eddies are usually caused by an obstruction in the river, such as a rock or fallen tree. This interrupts the main flow of the river, causing the eddy, which is usually on the downstream side of the obstruction.

Eddies are relatively small, contained pockets of moving water that break off from the main body of a current and travel independently of their parent. They can form in almost any part of a current, but are especially pronounced in western boundary currents.

Eddies are rotating masses of water in the ocean that typically form along the boundaries of ocean currents. In the Gulf of Alaska, eddies of warm water, filled with nutrients from shallow coastal water, mix with the cold water off the continental shelf.

Eddies are areas where water flows back upstream against the current. An eddy might be a good spot for entering and exiting the water safely, because you won’t have to deal with a strong current while clambering in and out. You will often find an eddy downstream from a large rock, and this will enable you to swim upstream.