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The author believes winter navigation, if initiated, could pose a serious threat to wintering waterfowl for three major reasons. One reason is that ice-breaking activities could cause ice to be diverted to areas that were previously ice-free during winter. Areas that are susceptible to being covered by diverted ice include important foraging sites for wintering waterfowl. This could decrease waterfowl food availability. Winter shipping may adversely affect food abundance by the resuspension of fine substrates. The coarser substrates left behind could limit important waterfowl foods. There is evidence that waterfowl wintering on the Detroit River were depleting their endogenous energy reserves even when critical shallow water depths were available for feeding. Loss of feeding habitat due to long periods of ice cover may force major portions of the population to either migrate with low lipid reserves, or starve to death.