Abstract: A system for cleaning water in rivers or lakes or for separating oil and water. The system includes a sucking pipe; vapor-liquid mixing device connecting to the sucking pipe; a pressure pump disposed midway of the sucking pipe; a compressor connected to the connection between the pressure pump and the vapor-liquid mixing device; a pressure tank connected to the vapor-liquid mixing device; a feed pipe connected to the pressure tank; and a pressure valve, attached to the leading end of the feed pipe, which opens at a pressure exceeding a predetermined level. According to this system, the construction can be simplified, and the lifting action by the bubbles can be effected by keeping the pressure of the liquid at a predetermined level or more at all times. Thus, the system can be used anywhere under all circumstances.