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Look: Extreme heat, low rainfall trigger massive fish kill in northern Philippines
Prolonged extreme summer heat followed by sudden downpours triggered fatal thermal shocks, depleting oxygen levels and leaving fish gasping at the surface in a phenomenon known as hypoxia
- PUBLISHED: Sat 27 Jun 2026, 6:00 AM
Extreme heat and sharply reduced rainfall have triggered a massive fish kill in northern Philippines, according to the country’s fisheries authority. Tonnes of freshwater fish, including tilapia and bangus, have died and floated to the surface, affecting the livelihood of hundreds of aquaculture operators in Magat Dam Reservoir in Isabela province, north of Manila.
Magat Dam’s fish kill was preceded by a similar incident in nearby Cagayan province last week, where fish cage operators in the town of Sanchez Mira reported massive fish kill of milkfish (bangus) due to critically low dissolved oxygen levels reported at the Pata River.
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Operators in the towns of Binmaley, Bolinao and Anda in Pangasinan province also lost this month as much as P15 million (nearly Dh 1 million) to another bangus fish kill incident.
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Caused by hypoxia
According to the Philippine Bureau of Fisheries and Aquatic Resources (BFAR), prolonged extreme summer heat followed by sudden downpours triggered fatal thermal shocks in the country's prized milkfish, causing oxygen depletion that left the fish gasping at the surface in a phenomenon known as hypoxia.
These incidents typically coincide with extreme weather, where prolonged heat causes a sharp drop in dissolved oxygen levels, or when sudden heavy rains follow hot, humid days, resulting in fatal thermal shock to the milkfish, BFAR added.
Magat Dam manager Engr. Gileu Michael Dimoloy told reporters the extreme heat index and low water level caused lower than normal dissolved oxygen levels in the water.
“When a fish kill starts, there is pollution in the water that can cause a domino effect and affect other fish cages in the area,” Dimoloy explained.
While the entire Philippines experienced normal to above normal rainfall conditions from March to May last year, the numbers plummeted to “way below normal” conditions in 78 of the country’s 82 provinces from March to May this year.
BFAR spokesperson Nazario Briguera assured authorities are assisting fish cage operators in harvesting remaining stocks in the reservoir and sell them to local markets.
The fish cage operations in the area significantly contribute to fish supply in the largely landlocked Cagayan Valley Region of the Philippines. They are, however, mostly operated by small-scale owners who lack modern technology such as solar-powered aerators to maintain healthy oxygen levels in the water.
Laws allow 10 per cent of the 4,500-hectare reservoir to be utilised for aquaculture, producing as much as 35 metric tons of freshwater fish daily. Currently, it averages roughly 0.8 metric tons of tilapia daily due to environmental conditions and stricter regulations.