The confession came after a preliminary investigation traced the birthplace of some of the dead pigs found in a section of the river in Shanghai to Jiaxing, the Jiaxing city government said, according to state-run Xinhua news agency.
The Jiaxing city government has said a total of 70,000 pigs died due to crude raising techniques and extreme weather at the beginning of the year.
They added that all the collected corpses were disposed of safely, and no mass swine epidemic had broken out in the region.
So far, Shanghai has provided 14 ear tags collected from the dead pigs, and Jiaxing is still investigating 13 of these tags.
Local media had previously reported that the corpses may have come from the upper reaches of the Huangpu River in Jiaxing City.