Yes! Even though Northern California is not really known for harsh winters, our water temperatures get cold enough to stop feeding. As water temperatures approach 50* F your Koi fish ability to digest food is greatly reduced. Koi enter a state of semi-hibernation and their body functions including the need for food decrease. Koi do not have stomachs, the food they consume is digested in their intestines. Feeding in the winter can cause bacterial infections in the gut. Do not feed your Koi fish below 50*!