MANILA, Philippines — An oceanographic phenomenon called upwelling caused the fish kill in Manila Bay along the Baseco seawall in Tondo, the Bureau of Fisheries and Aquatic Resources (BFAR) said over the weekend.
The BFAR said upwelling or overturn caused the depletion of dissolved oxygen, causing mortality of at least 10 kilos of fish in Manila Bay.
Photos of the dead fish went viral on social media last week, raising questions on whether the white sand project caused the fish kill.
The Department of Environment and Natural Resources has denied that the fish kill was caused by the crushed dolomite laid over a portion of Manila Bay for its rehabilitation program, which drew criticism.
Upwelling happens when saturated, cold seawater rises from below and replaces lighter and warmer water on the surface after a rainfall, according to the BFAR.
The upwelling water activity draws up sediments from the sea bottom bringing up organic load, which competes with fish in consuming available dissolved oxygen.
“With dissolved oxygen in the seawater depleted, the fish easily succumbed to choking,” the BFAR said.
The results of water quality analysis conducted by the BFAR in Baseco indicated a low level of dissolved oxygen at 0.11 milligram per liter. The acceptable level of dissolved oxygen for marine water is 5 mg per liter.
Aside from Baseco, the BFAR also conducted water quality tests at the Pasig River mouth area, Barge Docking and Aplaya sites.
Last week, residents of Baseco found biya, kanduli, asohos and tilapia “gasping for air” following heavy rains. The BFAR explained that these are bottom and midwater species, which easily succumb to choking as a result of dissolved oxygen depletion.