Compare lakes with seas.

Lakes and seas are very different. The seas must be connected to the oceans, they are much larger, have a coastline with continents or islands. All seas are salty, you cannot drink their water without special treatment. All seas are parts of the World Ocean, and animals can move from one to another practically without obstacles. The lakes are smaller, surrounded on all sides by land. These are closed ecosystems (in a place with rivers that fall or begin from them). There are both freshwater and salty lakes.