To kill red water and simultaneously feed oxygen to contaminated water in a nutrient-rich state clean the water.

In a water jetting ship by which water sucked from a ship bottom is jetted through a jet nozzle 2 provided on a ship board, compressed air under higher pressure than it of the injection jet is jetted from a compressor 6 during the injection jet. The injection jet is crushed with the compressed air and aerated, and also plankton can be killed with high pressure waves generated by rapid expansion of the compressed air and the contaminated water is cleaned.