Seiche, a temporary rising and falling of water that occurs occasionally in lakes and certain coastal waters. The phenomenon may last from a few minutes to a few hours, with the change in water level varying from one or two inches (2.5 to 5 cm) to two feet (60 cm) or more. Seiches have long been known in Europe and were observed scientifically on Switzerland's lakes as early as the 16th century. They have since been found to occur throughout much of the world. They are seldom destructive.

The causes of seiches include storms, winds, and earthquakes. Probably the most common cause is a rapid change in barometric pressure, usually as a result of a storm passing over the body of water. The sudden drop in air pressure over one part of a lake, for example, causes the water level there to rise temporarily, with a corresponding lowering of the water elsewhere in the lake.