There’s nothing to worry about the massive fish kill and shellfish mortality in Las Piñas, Parañaque, Bacoor, Cavite since the incidents were due to “natural causes,” officials of the Department of Environment and Natural Resources (DENR) assured on Thursday.
This, even as the Department of Agriculture, through its Bureau of Fisheries and Aquatic Resources (DA-BFAR), earlier declared that the fish kill could have been caused by the high levels of ammonia and phosphate in the waters of Manila Bay, on top of the low concentrations of dissolved oxygen, particularly in Las Piñas and Parañaque City.
DENR officials also said that the water quality in Las Piñas and Parañaque where the fish kill was observed have improved, while shellfish gathering in mussel farms in Bacoor and Sangley Point is “back to normal.”
Initial water quality test results conducted by the DENR confirmed the 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,” Environment Secretary Roy Cimatu said in a news statement.
Citing results of the laboratory tests conducted by the DENR, Cimatu said the DO for 3 out of 4 stations in the Las Piñas-Parañaque Wetland Park did not conform to the water quality guidelines (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 Environmental Management Bureau-National Capital Region (EMB-NCR) Director Domingo Clemente, 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 (the boundary of Long Island and Freedom Island, approx. 30 meters from the shoreline), 5.9 mg/L; and Station 4 (Freedom Island, approx. 30 meters 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. Station 2 recorded the highest concentration of fecal coliform at 350,000 MPN/100 ml, while the levels in the three other stations ranged from 23,000 to 24,000 MPN/100 ml.
The DENR report did not say whether it conducted similar tests for ammonia and phosphate which the DA-BFAR had found and identified as the cause of death of the assorted fish species that could reach up to 5,000 kilos.
Nevertheless, the DENR official said 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 days after the fish kill on November 8, 2019, 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, a significant increase in the DO was observed in Stations 1, 2 and 3, and all stations passed the WQG,” Cimatu said.
“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,” he said.
The EMB-NCR and the LPPWP management inspected the area and interviewed some fishermen who claimed the shellfish mortality was brought about by the phenomenon they call alig.
“The fisherfolk said that it was due to alig, a natural phenomenon characterized by the mixing of freshwater and saltwater, 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.
During the inspection, Clemente said, they observed the ongoing harvesting of mussels in the area, which indicates that fishing business there “is back to normal.”