Waterspouts are a type of whirlwind comprised of rapidly rotating columns of air that form over lakes or, rarely, oceans. They look like tornadoes, connecting a cloud to the surface of a body of water.
Unlike tornadoes, waterspouts don't necessarily require severe thunderstorms to generate or continue their motion. A tornadic waterspout is just like a tornado, only on water, and happen in the most exceptional situations. The more common waterspout is non-tornadic. These are caused by an updraft meeting a water rotation near the surface of the body. In this case, a funnel of rotating air is formed between the surface of the water and the base of a (typically congestus) cloud. They are fairly common in late summer and early fall, when the warm surface temperatures combine with cold air currents to create strong updrafts and instability in the weather.
While there can be a cluster of waterspouts, they are typically single entities. Although waterspouts are wet, they aren't actually lifting much water from the lake or ocean; rather it is the condensation of the low air pressure inside the funnel which produces the wetness. Waterspouts usually begin as a shadow or dark spot on the water, where rotating air is distorting the surface. In no time at all, the fully formed waterspout will begin to curve along the water until cooler air enters the funnel and causes it to dissipate.