Local fishery authorities in east China's Fujian Province said Tuesday a lack of oxygen caused the deaths of 15,500 tonnes of fish discovered in a major river.

A test showed that the amount of dissolved oxygen in a section of the Minjiang River flowing through Gutian County was an average of 1.2 milligrams per liter of water, which is only a quarter of what is needed for fish to survive, according to an investigation report released by the provincial department of oceans and fisheries.

The low oxygen levels were connected to heavy downpours brought by Typhoon Nanmadol in late August, the report said.

The dead fish, all artificially bred in net cages, were found in the river in the townships of Shuikou and Huangtian in Gutian between Aug. 28 and Sept. 3, according to a spokesperson for the provincial department of oceans and fisheries.

By Sunday, fish from 8,800 cages owned by over 800 fish farmers in the two townships had been found dead, creating direct economic losses of 186 million yuan (about 29.1 million U.S. dollars), said the spokesperson.

The Minjiang River, spanning over 500 kilometers, is the largest river in Fujian.