The ballast water contains many planktons, fish eggs, etc. which sometimes gives a detrimental effect on the environment where thousands miles away from the ballast water is loaded. The present experimental study showed that the high-speed water flow could destroy planktons. The generation of cavitation should increase the effect of destruction. We examined two methods; those were two nozzles in a pipe, and cavitating jet flow into a chamber. Both were promising and should continue the experiment to find the best set-up to destroy planktons.