The number of dead pigs found in a river near Shanghai rose to more than 13,000 over the weekend. Last Friday, the figure stood at about 7,500. The authorities, who are in the middle of a weeklong effort to collect the carcasses, are still trying to determine how the pigs died and why they ended up in the Huangpu River, which winds through Shanghai. The government has insisted that there is no evidence of an epidemic and that the food supply is safe. City officials also say the river meets national water quality standards. The authorities say they believe that many of the pigs came from the nearby city of Jiaxing, in Zhejiang Province, where there are major pig farms.