The vessels, carrying a total of 4,000 tonnes of what police suspect to be household garbage, were seized in Jiangsu Province last week, following online reports of garbage from nearby Shanghai being dumped there.
More than 20,000 tonnes of waste consisting mostly of construction materials were found across 2,400 square meters of the bank, according to local authorities.
Police are investigating the case, state-run Xinhua news agency reported.
Water samples collected from the area around the dumping site tested normal, the local environmental bureau said.
Police said these vessels carried the garbage from Jiading, a suburban district in Shanghai.
The vessel owners said the garbage was loaded onto their boats in Jiading and would be collected by a construction firm once it was dumped in Taihu.