Seas are often defined by connection to the ocean or another sea via salt water, which the Caspian Sea is not. Seas are usually partially enclosed by land, according to the National Oceanic and Atmospheric Administration, but the Caspian Sea is entirely enclosed by land. Seas are typically salt water. While the Caspian Sea is not fresh water, its salty water is diluted by the inflow of fresh water, especially in the north.