可以参考维基百科对海和湖的解释, 海是大洋的一部分, 而湖不是...湖主要靠河流补给, 而海不是...一般来说, 海是咸水水体...
当然, 这些都不是非常严格定义的...
http://en.wikipedia.org/wiki/SeaThe term sea refers to certain large bodies of water, but there is inconsistency as to its precise definition and application. Most commonly, a sea may refer to a large expanse of saline water connected with an ocean, but it is also used sometimes for a large saline lake that lacks a natural outlet, e.g. the Caspian Sea. Colloquially, the term is used as a synonym for ocean. Additionally, large lakes, such as the Great Lakes of North America, are occasionally referred to as "inland seas".
-----------------------------
http://en.wikipedia.org/wiki/LakeA lake (from Latin lacus) is a terrain feature (or physical feature), a body of liquid on the surface of a world that is localized to the bottom of basin (another type of landform or terrain feature; that is, it is not global) and moves slowly if it moves at all. On Earth, a body of water is considered a lake when it is inland, not part of the ocean, is larger and deeper than a pond, and is fed by a river.[1][2] The only world other than Earth known to harbor lakes is Titan, Saturn's largest moon, which has lakes of ethane, most likely mixed with methane. It is not known if Titan's lakes are fed by rivers, though Titan's surface is carved by numerous river beds.
Natural lakes on Earth are generally found in mountainous areas, rift zones, and areas with ongoing or recent glaciation. Other lakes are found in endorheic basins or along the courses of mature rivers. In some parts of the world, there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them.
