Bangkok Governor Apirak Kosayodhin yesterday ordered the city's internal drainage system to be closed off to the Chao Phya River as the pulse of polluted water which killed thousands of fish in Angthong would reach Bangkok today.

He asked the Irrigation Department to release more clean water from the Chao Phya and Rama VI dams into the river to dilute the contaminated flow before it enters Bangkok.

He told all 50 district chiefs to inspect factories along the river to prevent them from discharging untreated wastewater into the channel.

Samart Chokekanapitak, director-general of the Irrigation Department, said the Chaipattana Foundation had offered the use of 36 aerators which would be installed anywhere along the Chao Phya upon request from local administrations.

He said the huge mass of polluted water, about one kilometre long, was in Ayutthaya's Bang Sai district and the quality was not as bad as when it was in Angthong.

The ratio of dissolved oxygen in the polluted water had improved somewhat from below one milligram per litre to 1.26mg/l. The level required by the Pollution Control Department to ensure the survival of marine life is 6mg/l.

Ayutthaya Governor Cherdphan na Songkhla hired a company to treat the water with micro-organisms.

Chawalit Sarun, deputy governor of the Provincial Waterworks Authority for Area 5, ordered his Ayutthaya and Pathum Thani offices to prepare more activated carbon and chlorine to treat raw water used to produce tap water.

He said the mass of polluted river water was only eight kilometres away from the Bang Sai filtering plant in Ayutthaya.

The tap water supplied to the two provinces is still safe to drink, he said, adding that scientists were posted at the two provincial offices to analyse the quality of tap water every day.