Natural causes appear to be the reason for the deaths of thousands of fish in the Las Piñas-Parañaque Wetland Park (LPPWP) last October 10.
Environment Secretary Roy A. Cimatu said the initial water quality test results revealed that the fish kill resulted from low concentrations of dissolved oxygen (DO) in the water.
“Fish, like all other complex life forms, need oxygen to survive. They get theirs in the form of oxygen gas dissolved in the water,” Cimatu said.
The DENR Secretary said the results of the laboratory tests conducted by the Environmental Management Bureau (EMB) on October 10 showed that the DO for three out of four stations in LPPWP did not conform with the water quality guideline (WQG) for Class “SB” waters, which is 6 milligrams per liter (mg/L).
Dissolved oxygen is the volume of oxygen that is contained in the water and is vital in supporting aquatic life, while Class SB water classification means that the water is “suitable for commercial propagation of shellfish and intended as spawning areas for milkfish.”
According to EMB-National Capital Region Director Domingo Clemente, the low levels of DO “may have resulted from the recent heavy rains that caused the flushing of decomposed organic matter from the surface run-offs and inland water tributaries eventually polluting the open seas.”
Based on the results, the DO for Station 1 (Long Island, approximately 30 meters from shoreline) was 3.3 mg/L; Station 2 (Long Island, approx. 20 meters from shoreline in front of Pier Area), 3.4 mg/L; Station 3 (boundary of Long Island and Freedom Island, approx. 30 meters from shoreline), 5.9 mg/L; and Station 4 (Freedom Island, approx. 30m from shoreline), 9.8 mg/L.
All four stations also exceeded the WQG for fecal coliform, which is 100 most probable number per 100 milliliters (MPN/100ml). Station 2 recorded the highest concentration of fecal coliform at 350,000 MPN/100ml, while the levels in the three other stations ranged from 23,000 to 24,000 MPN/100ml.
Traces of cyanide—a chemical that is lethal to most fish species and invertebrates as it blocks the absorption of oxygen by cells and causes the species to suffocate and die—were also found in all four stations, exceeding the WQG of 0.02 mg/L for Class SB waters.
Cimatu, however, said the water pollution measures showed improvement during the follow-up tests conducted on October 14 or just four days after the fish kill occurred.
He said the DO concentrations increased and the fecal coliform levels went down significantly.
“Based on the results of the follow-up tests, significant increase in the DO was observed in Stations 1, 2 and 3, and all stations passed the WQG,” Cimatu said.
He added: “Also, the results of the fecal coliform count decreased, which now range from 540 to 1,600 MPN/100ml from a high of 350,000 MPN/100ml on October 10.”
Cimatu said the Department of Environment and Natural Resources (DENR) will continue to monitor the water quality levels in LPPWP to ensure it would not affect the rehabilitation efforts in Manila Bay.
Last October 11, personnel from the DENR, city governments of Las Piñas and Parañaque, and the “bakawan warriors” assigned to LPPWP cleared the shore of dead fish, which were causing a heavy stench in the area.
They were able to gather more than 200 sacks weighing over 5,000 kilos of different marine species, such as fish, shrimps and crabs.
The dead fish were hauled out and brought to the Las Piñas Transfer Station, and not buried at LPPWP as earlier reported.
On October 17, the EMB-NCR and the LPPWP management inspected the area and interviewed some fishermen who claimed the fish kill was brought about by a phenomenon they called “alig.”
“The fisherfolk said that it was due to alig, a natural phenomenon wherein the freshwater and salt water mix, in addition to continuous rains and rising water temperature,” Clemente said.
“Also, the concentration of the death of mussels was only in the outskirts of Barangay Longos and Barangay Sineguelasan,” he added.