Authorities in Shanghai, China, pulled several hundred pig carcasses from the Huangpu River on Saturday. The river is a source of drinking water for the city. Nearly 9,000 dead pigs have been fished from the river since early March.

In nearby Jiaxing authorities have found over 3,600 dead pigs.

The phenomenon is believed to be linked to a police crackdown on illegal trade in pork from diseased animals. Pig breeders are not compensated for loss due to animal illness, and therefore face pressure to sell them despite their disease, or at a minimum to save the costs of proper disposal.