Local government workers gather dead fish for disposal after being washed overnight along the coastline at the reclaimed 'Freedom Island' in suburban Las Pinas city south Manila, Philippines. Image Credit: AP

Manila: Polluted water has been blamed for the massive fish kill that lined the shores of the cities of Las Pinas and Paranaque in Southern Metro Manila in recent days.

According to the Bureau of Fisheries and Aquatic Resources (BFAR), tests conducted on water samples collected from the two cities showed low amounts of dissolved oxygen and other imbalances.

“The water quality test conducted in three sampling areas by BFAR’s National Fisheries Laboratory Division and BFAR 4A [Region 4A or the Cavite, Laguna, Batangas, Rizal, Quezon corridor] shows poor levels of dissolved oxygen and higher levels of ammonia and phosphates than the standard level,” BFAR said in a statement.

On October 9, residents were surprised to find thousands of dead fish washed up on the shores of Las Pinas’ Long Island, and Paranaque’s Freedom Island, which are marine protected areas.

Agriculture Secretary William Dar ordered BFAR on the following day to assess the water quality in the area. Authorities were also able to collect about two tonnes of dead fish from the shores of the two cities.

Reports said that among the fish species found washed up on the shores were asuhos (silago), kanduli (marine catfish), butete (blowfish), sapsap (ponyfish), tilapia and barracuda.

Based on assessments, there was an apparent depletion of dissolved oxygen in the collected water samples.

BFAR said that to be considered “normal,” dissolved oxygen should be greater than five parts per million (ppm), but tests showed it was only 0.70 to 2 ppm.

The water samples also have high levels of ammonia at 3.59 ppm when the norm is less than .05 ppm.

Ammonia is a naturally occurring chemical given off by decomposing organic matter such as plants, animals and animal waste, however, in the case of the collected water samples, there are indications that these compound could have come from agricultural, domestic or industrial wastes.

Another element found in the tests is phosphates, which could come from raw domestic sewage, agricultural runoff or urban wastes.

Experts said it was likely that pollution, chemical, organic or otherwise that could be responsible for the fish kill.

While Las Pinas and Paranaque are among the most urbanised areas of Metro Manila, a considerable number of residents, particularly those living in coastal areas, rely on fishing for their livelihood.

The coastal waters of the two cities are also part of the Manila Bay.

It can be recalled that last year, President Rodrigo Duterte ordered the rehabilitation of the Manila Bay due to years of pollution and neglect.