lake (a large area of water surrounded by land): This lake is dangerous for swimmers.
lagoon (an area of water that is separated from the sea by a reef or sandbar): The water in the lagoon was calm.
pond (a small area of fresh water formed naturally or created artificially): The ducks were swimming on the pond.
pool (a small area of still water that has formed naturally): The water collected in a little pool near the summit of the mountain.
reservoir (a natural or artificial lake where water is stored before it is supplied to people): Water is piped from this reservoir to the city.
puddle (a small pool of water, especially from rain): Don’t drive through that puddle.