SUDDEN FISH DEATHS ALARM COMMUNITIES: CamSur fish kills blamed on ammonia, low oxygen

Over P500,000 in losses reported

in Calabanga, Tinambac towns

By Rhaydz B. Barcia and Connie Calipay

LEGAZPI CITY --- A series of fish kill incidents in the waters of Camarines Sur, particularly in San Miguel Bay, have been attributed to a dangerous mix of rising sea temperatures, high ammonia levels, and poor water quality, according to the Bureau of Fisheries and Aquatic Resources (BFAR) regional office.

BFAR-Bicol spokesperson Rowena Briones said that three separate fish kill events were reported in Kawit Island in Barangay Cagsao, Calabanga, and in the coastal areas of Bagacay, Sta. Cruz, and both New and Old Caaluan in Tinambac town between May 23 and 24, 2025.

The incidents caused the death of approximately 3.5 tons of various fish species and crustaceans — 2 tons in Tinambac and 1.5 tons in Calabanga — resulting in an estimated economic loss of P512,500.

Initial water tests conducted on May 23 yielded mostly normal results, except for elevated ammonia levels. However, a follow-up assessment on May 26 revealed significantly deteriorated conditions in three affected sites.

“The dissolved oxygen levels were extremely low, ranging from just 0.18 to 2.07 parts per million (ppm), far below the safe threshold of 5 ppm,” Briones said. “Hydrogen sulfide levels were also alarmingly high, between 58.9 and 280 milligrams per liter, when the acceptable limit is only 0.002 mg/L.”

Turbidity and ammonia levels were also found to be excessively high, which BFAR linked to organic waste accumulation and weakened water currents — particularly in the shallow, semi-enclosed areas of San Miguel Bay. The combination of these factors created lethal conditions for marine life.

Briones explained that hot weather lowers oxygen levels in water, and sudden heavy rains after extreme heat can cause temperature shock and disturb sediments on the seabed, further reducing water quality.

Ammonia build-up, she said, often results from decaying marine debris, plant matter, and other organic materials that settle on the seabed, especially in areas with limited water movement.

The fish kill incidents subsided on May 26, but BFAR Bicol continues to monitor the affected zones in coordination with the local governments of Calabanga and Tinambac. Field surveillance and regular water assessments are ongoing to prevent a recurrence.

Fish samples collected from the affected areas are being flown to BFAR’s central office for laboratory testing to determine any other contributing factors to the die-offs.

Meanwhile, the Calabanga Fisheries Management Unit has warned residents against harvesting or consuming dead fish found in local waters as a safety precaution.

Meanwhile, the Bureau of Fisheries and Aquatic Resources in Bicol (BFAR-5) has begun a series of water quality assessments in two towns in Camarines Sur after a fish kill was reported.

In a phone interview on Friday, BFAR-5 spokesperson Rowena Briones said the fish kill on May 23 and 24 affected parts of Calabanga and Tinambac towns and resulted in the loss of approximately 3.5 tons of various fish species and crustaceans.

“We are closely coordinating with the local government units (LGUs). For now, the LGUs are assisting the affected fisherfolk. The estimated damage costs amount to PHP512,500. The fish kill occurred in the wild areas of Kawit Island, Cagsao, Calabanga, Old and New Caaluan, Sogod, Mananao, and Tinambac. We are continuously monitoring the affected areas through regular water quality assessments and field surveillance to track environmental conditions, assess ongoing risks, and implement timely mitigation measures,” Briones said.

Briones said the BFAR has already collected fish samples following the incident, which are still undergoing laboratory examination to help determine all possible causes.

“We are awaiting the (final) results, as they have already been submitted to the BFAR Central Office in Manila,” she added.

She said initial test results indicated that deteriorated water quality parameters are likely contributing to the observed fish mortality in the area.

“There are low levels of dissolved oxygen in surface, middle, and bottom water samples across all stations, ranging from 0.18 to 2.07 ppm, which is far below the ideal threshold of 5 ppm. Hydrogen sulfide levels were found to be between 58.9 and 280 mg/L, vastly exceeding the desirable limit of 0.002 mg/L. Turbidity and ammonia levels were also notably high,” she added.

Briones urged the public, coastal communities, fisherfolk, and local government units to actively participate in the protection and sustainable management of aquatic resources. This includes adhering to fishing regulations and practicing responsible and sustainable fishing techniques.

“We recommend that fish affected by the fish kill should not be consumed. However, fish that are freshly harvested and alive in the areas are safe to eat,” she added.

Briones said one possible cause of the low dissolved oxygen levels is the hot weather, as oxygen is scarcer in warmer waters. The demand for oxygen by the fish and other marine life increases when water temperatures rise.

She also added that sudden rain following hot weather can cause temperature shock to marine life.

“Especially if the rain is heavy, sediments on the seabed can be agitated, increasing turbidity. The cold rainwater will sink, causing water from the bottom to rise. In such cases, the water at the bottom typically has low dissolved oxygen, which can deplete the oxygen levels even further,” she said.