PURPOSE: To provide the subject controlling agent containing chlorine dioxide, etc., as an active component, exhibiting excellent effect to prevent the adhesion with relatively small amount of the agent, usable without generating trihalomethane, free from residual and cumulative toxicity and environmental pollution and useful for preventing the adhesion of aquatic life in seawater, etc.

CONSTITUTION: The objective agent contains, as an active component, chlorine dioxide (ClO2) having high water-solubility and an available chlorine content corresponding to 2.6 times that of chlorine or an agent for generating chlorine dioxide. The active component may be used as it is, compounded to form a composition or supported on a carrier. The amount of ClO2 is ≥0.015ppm based on water. The chlorine dioxide-generating compound is e.g. an alkali metal chlorite, especially NaClO2 and the amount of the compound is ≥0.025ppm in terms of NaClO2. Since NaClO2 generates ClO2 upon addition of a strong acid, hypochlorous acid, oxidizable substance, etc., it is preferable to allow the compound to quickly contact with the reactive component after the addition to water. The available chlorine-generation process of ClO2 is supposedly the oxidation reaction of ClO2- shown by the reaction formula.