Answer: The only information I can find is that the main problems of Koi with lilies result from the inquisitiveness of the fish. Lilies hate being disturbed. Leaf stems and flower bud stalks are easily damaged by fish rubbing up against them. The fish also love to delve in the soil in the containers in which the lilies are planted, giving the pool water an unattractive beef consomme look. And, Koi ponds are usually pretty deep - too deep for water lilies. I cannot find any other reason, but you may want to check with a Koi expert to make sure these are the only reasons to keep water lilies away from Koi.
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