Orders have been issued to cut off water supply and drainage connections to these units and they have been asked not to release effluents in the Daman Ganga river. The action follows a survey undertaken by pollution control board authorities following complaints of a foul smelling gas and high incidence of fish mortality in the river and the Arabian sea.

Last week residents of the Vapi industrial estate and nearby areas complained of a foul smelling gas, the source of which remains elusive till date. A GPCB official said the foul smelling gas could be ethyl mercaptan. It maybe noted that similar complaints of a foul smelling gas were made in Surat and Ahmedabad a few days ago.

Sources, however, said it was possible that the gas could have leaked from tankers going to Daman.

Even when the pollution control authorities were struggling to locate the source of ethyl mercaptan came the news of hundreds of dead fish in Kacchigam, where the river meets the sea. The rotting fish on the banks forced the pollution control board authorities from Vapi and Daman out of their slumber.

The GPCB team which collected samples of effluents found that they had grossly violated the Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) norms.

It was found that many units were releasing chemicals into the river that led to the death of hundreds of fish.

As many as 14 units from Vapi were found releasing phenol into the water and were served notices for polluting water while two other units were found polluting the air. All have been booked under respective legislations. Regional officer A A Dolti said the units were found releasing chemicals which dissolve oxygen in the water. He, however, said there were other chemicals too, some stronger, which contribute to the phenomenon, which denies fish oxygen.

He said the board got in touch with Daman pollution control authorities when it was found that a couple of distilleries in the Union Territory were polluting water. Daman-based Member Secretary of the pollution control committee Dr Suryaprakash said samples drawn from the two distilleries had been sent to the Central Pollution Control Board's Vadodara office.

The report was expected by Tuesday night. He said samples of dead fish were also sent outside for laboratory tests to determine what exactly caused their death. The reports may take some time, he said.