No danger at all. Nature is designed perfectly to take care of such a situation, even down to the bones. Only threat to water quality is if the animals die in an active drainage. Full grown cow only lasts about 3 days around here before the predators have it stripped to the bone.
Had a Florida deer (not Key deer, those are even smaller) get killed by a car right by my house one morning. By the time I came home at lunchtime, it was nothing but a skeleton. Turkey vultures are quite efficient.