Tip: See my list of the 
MostNon-native speakers of English sometimes incorrectly say that a non-living thing, such as a boat or a piece of wood, “swims in the water” because that’s the way they would say it in their native language.
In English, however, only a living thing (such as a person or an animal) can swim, because swimming is an intentional activity, not something that is being done to a person or a thing (but there are a few exceptions mentioned at the end of the article). When a non-living thing moves in a river simply because it is being carried by the stream, the correct verb to use is float:
Living things can also float when they don’t intentionally move and don’t sink, as in
(note that “lay” is the past tense of “lie” here). But what when you speak about a ship or a boat? Ships typically do not just float; they are operated by humans in order to move from one place to another. The correct verb to use in connection with a boat or a ship is sail (but using a generic verb like “go” or “travel” is fine too, of course):
It may seem strange to use the verb “sail” to speak about ships that have modern engines and propellers, but that’s just the way the verb has been used since the times when all ships had sails.
But what about submarines? Submarines never had sails (even in the past), but it turns out that the same verb was also extended to them:
Another, somewhat less common verb used in connection with submarines is “cruise” (e.g. “the submarine cruised to Pearl Harbor”).
Exceptions
When I wrote that “only a living thing can swim”, it was not the whole truth. When referring to robots (both autonomous and remote controlled) that can move in water, it is commonly said that they swim, even though they are not living beings in the traditional sense of the word.
The verb “swim” can also be used figuratively to express that something is covered with a large amount of liquid, e.g.
It can also be used to describe things moving around you, especially when you feel dizzy, for example,
