Sail, paddle, or row a boat ON a river, a lake, the sea, or the ocean. "I saw five tall ships sailing on he ocean" Swim IN a river, a lake, the sea, the ocean. "Bob goes swimming in the ocean every morning."

(U.S. English) Unless we are discussing the 7 named oceans specifically, it is always "the ocean." singular If you are talking about what is going on under the surface of the water, such as swimming, it is "in the ocean." It would not be common to say "on the ocean" unless you were speaking scientifically about something affecting a vast portion, or all, of the ocean. You can tell a child to put their boat "in the water," "out on the water" if it is farther, or that a ship sailed the many seas/waters. The plural is used to imply crossing boundaries of multiple bodies of water. Yet, it is still not commonly used for ocean.

Thank you，I forgot it.

How DO we normally say this? Why DO you cook fish that long? Where DO you work? How many DO you have? Who DO you want to win? What DO you like to read? When DO you find time to paint? I- do (singular & plural) you- do he/she/it/name- DOES we- do they- do