At a press briefing in Hanoi on May 14, Tac said all evidence pointed to the two most likely causes of toxic substances and algae, adding that other causes from seismic impact, heat shock and diseases have been ruled out.
This was the results of more than a month of research by domestic and foreign scientists from Japan, Germany, France, the US and Israel, he said, noting that the Ministry of Science and Technology had established a Council of Scientific and Technological Experts for the purpose together with teams working in the four affected provinces.
The mass fish deaths were as first reported in the water area off Vung Ang Port and Ky Anh township in the central province of Ha Tinh on April 6. The phenomenon later spread to Quang Binh on April 10, Thua Thien-Hue on April 15 and Quang Tri on April 16, and lasted till May 4.
On April 24-26, brown sea tide was also spotted in the region.
Then on May 4, a streak of reddish sea water appeared along the shoreline of a beach in Quang Binh, but it has faded away several days later.