Water Following its use as an aquatic herbicide at normal application rates, diquat residues in water have been found to decrease rapidly to essentially undetectable levels within 7-14 days (section 4.3). Toxic effects on fish and other living organisms in the water are unlikely, because diquat is rapidly photodegraded, absorbed by aquatic weeds, or adsorbed to soil particles at the bottom. However, caution should be taken in the application of diquat to water containing heavy weed growth, since oxygen consumed by subsequent weed decay may decrease the oxygen content of the water to such an extent that it is dangerous for fish or other aquatic organisms. No phytotoxic damage should occur on crops irrigated with diquat-treated water, if at least 10 days is allowed to elapse between treatment and irrigation.