Mass mortality of ducks occurred in the duck farm rented by the plaintiff. Tests indicated that cyanide was found in the livers of ducks. Therefore the plaintiff claimed that the mortality was caused by the polluted water released by the defendants, three companies upstream. The court held that, in accordance with the article 66 of the Tort Law of the People's Republic of China, the inversion of burden of proof in environmental pollution cases does not preclude the initial burden of proof on the plaintiff to prove the preliminary causation. Since the plaintiff failed to prove that the cyanide was drained by the defendants, the tort liability was not established. The court thus dismissed the plaintiff's claim.