MANILA, Philippines—A long slick of oily substance was found floating in Pasig River at the Manggahan Floodway in Pasig City Friday prompting city officials to suspect that one of the establishments along the riverbanks may have leaked chemicals.

Two Pasig offices -- the city environment and natural resources office (CENRO), and the sanitation and waste management office -- are now investigating the oil spill at that portion of the Pasig river.

The oil spill was reported to Pasig's Rescue 211 Thursday evening by Manggahan residents who complained of a foul smell in the river, which they likened to a gas leak.

City sanitation officials have already plied the Manggahan Floodway, covering three riverside villages -- Manggahan, Maybunga and Rosario -- to trace the origin of the leak.

Rainier Peralta, sanitary inspector, told the Philippine Daily Inquirer that the spillage covered the whole stretch of Manggahan and ended in Maybunga.

"We suspect that it is some form of a liquid waste," said Peralta.

Authorities are still set to test a bottled sample of the leakage to identify who may be responsible for the discharge.

"One of the establishments near the river may be a possible cause for the spill," Engineer Reynaldo Tuozo, acting Pasig CENRO chief, said in an interview.

Tuozo said his office is currently doing the rounds of these factories to check on the waste materials in their establishments and determine if any of these match the spill sample.

Sanitation officials have also warned informal settlers under the Manggahan bridge against harvesting the swamp cabbage (kangkong) growing along the river border.

Peralta said the swamp cabbages are often harvested by the slum dwellers in the river for their own consumption or to sell in the nearby wet markets.

"We'd like to ask them not to harvest for now, this might cause food poisoning," said Peralta.