In late 2025 and early 2026, two separate algal bloom events in the Philippines — one in Misamis Oriental and another in Biliran — prompted local governments to issue public health warnings and restrict fishing and shellfish gathering. These incidents, while distinct in their causes and toxicity, highlight a recurring environmental challenge that affects coastal communities, marine ecosystems, and food safety across the archipelago.
Algal blooms occur when there is a sudden surge in algae density within an aquatic ecosystem. Some algae produce dangerous toxins, while others cause harm indirectly by depleting oxygen as they die off. Understanding the difference between these types matters for anyone living near coastal waters or relying on seafood. The Misamis Oriental event, for instance, involved Gymnodinium spp., a genus known to produce toxins that can accumulate in shellfish and cause paralytic shellfish poisoning in humans. The Biliran event, by contrast, involved a different organism entirely.
What Distinguishes Toxic From Non-Toxic Blooms
The core distinction comes down to how each bloom threatens marine life and human health. Toxic blooms pose a direct poisoning risk through contaminated seafood. Non-toxic blooms, while harmless if ingested, can still cause fish mortality by creating oxygen-depleted zones. Both types disrupt local fishing economies and require government intervention.
In Misamis Oriental, the Provincial Environment and Natural Resources Office (PENRO) confirmed the bloom through laboratory tests conducted by BFAR 10 on waters off coastal barangays Gracia and Baluarte in Tagoloan. BFAR issued an initial advisory on October 18, 2025, after discoloration was observed the previous day. The advisory warned against buying locally sourced shellfish, though it noted that fish, squid, crab, and shrimp remain safe to eat if properly cleaned and thoroughly cooked. Governor Juliette Uy instructed provincial departments to carry out a thorough assessment and develop a rehabilitation plan for the Misamis Oriental Provincial Agriculture Development Complex.
How Each Bloom Unfolded and What Officials Did
The two events followed similar patterns but diverged in their public health implications. In Misamis Oriental, the bloom of Gymnodinium spp. triggered an immediate shellfish ban because these algae can produce saxitoxins, which cause paralytic shellfish poisoning. Symptoms can include tingling, numbness, and in severe cases, respiratory paralysis. The PENRO reassured the public that properly cleaned and thoroughly cooked fish, squid, crab, and shrimp remain safe — the toxins concentrate in shellfish that filter-feed on the algae.
In Biliran, residents of the island municipality of Maripipi noticed green particles on coastal waters and shorelines on March 4, 2026. Municipal officials immediately asked the Philippine Coast Guard Sub-Station to collect samples for testing at the BFAR regional office. Tests showed the coloration was caused by a bloom of Noctiluca scintillans, commonly called “sea sparkle” because it produces bioluminescence when disturbed. Professor Leni Yap, a marine scientist at the University of the Philippines Tacloban, explained that this dinoflagellate does not produce toxins and is a natural phenomenon. However, BFAR-8 warned that its rapid increase can lead to decreased dissolved oxygen in the water, potentially causing fish mortality — especially for fish in cages and shellfish that cannot move away.
The local government issued a public advisory discouraging swimming in affected areas and temporarily disallowing fishing activities. It advised residents to wash fish thoroughly with running water and remove the intestines, and to refrain from eating shellfish for the time being. BFAR-8 clarified that the bloom “is not harmful or fatal to humans, as it does not contain toxins that are dangerous to people,” but emphasized the oxygen depletion risk to marine organisms.
What Gets Missed About Algal Bloom Causes and Responses
Several nuances about algal blooms are often overlooked in public discussion. Understanding these can help coastal communities respond more effectively and reduce future risks.
Nutrient Pollution as a Trigger
BFAR stated that the bloom of Noctiluca scintillans could be due to an increase in nutrient levels in the water, along with the effects of weather conditions. Excess nitrogen and phosphorus from agricultural runoff, untreated sewage, and industrial discharge feed algal growth. This means that blooms are not purely natural events — human activity on land directly influences what happens at sea. Reducing nutrient pollution through better waste management and agricultural practices can lower the frequency and severity of blooms. For a deeper look at how land-based pollution reaches waterways, see our article on septic issues and river pollution.
The Oxygen Depletion Time Lag
When a non-toxic bloom dies off, the decomposition process consumes dissolved oxygen. This can create dead zones that persist for days or weeks after the visible discoloration fades. Fish farmers may see losses even after the water appears to have cleared. Monitoring dissolved oxygen levels during and after a bloom event is critical for aquaculture operations.
Species Identification Is Not Instant
Visual observation alone cannot determine whether a bloom is toxic. In both incidents, local officials had to wait for laboratory results from BFAR before issuing specific advisories. This delay — typically a few days — creates uncertainty for fishing communities. Having rapid testing capacity in more coastal municipalities would shorten this gap.
Different Advisories for Different Seafood
In Misamis Oriental, officials explicitly stated that fish, squid, crab, and shrimp remain safe if properly cleaned and cooked, while shellfish were banned. This distinction matters because toxins accumulate differently across species. Filter-feeding shellfish concentrate toxins in their tissues, while fish and crustaceans metabolize or excrete them more quickly. Knowing which seafood is safe reduces unnecessary economic losses while protecting public health.
What Coastal Communities Can Do During a Bloom Event
When an algal bloom is reported in your area, taking the right steps quickly can protect your health and livelihood. The following actions are based on the advisories issued during the Misamis Oriental and Biliran events.
Check Official Advisories Before Harvesting or Buying Seafood
BFAR issues public advisories through local government units and media. Before gathering shellfish or buying from local vendors, confirm whether an advisory is in effect for your municipality. In Misamis Oriental, the warning specifically targeted locally sourced shellfish from Tagoloan waters. If you are unsure, contact your municipal agriculture office or the nearest BFAR regional office.
Handle and Prepare Seafood Properly
Even when an advisory allows consumption of certain seafood, proper handling reduces risk. Wash fish thoroughly with running water and remove the intestines and internal organs, where toxins may accumulate. Cook seafood thoroughly — though note that cooking does not destroy the toxins produced by Gymnodinium spp. in shellfish. For non-toxic blooms like Noctiluca scintillans, thorough cleaning and cooking are sufficient precautions.
Avoid Swimming and Fishing in Affected Waters
During the Biliran event, the local government discouraged swimming and temporarily disallowed fishing activities. Some algae can cause skin irritation or allergic reactions upon contact. Even if the bloom is non-toxic, the water may contain bacteria or other pathogens associated with the same nutrient pollution that triggered the bloom. Stay out of discolored water until officials declare it safe.
Report Discoloration to Authorities Immediately
In Maripipi, residents noticed green particles and reported them to municipal officials, who then coordinated with the Philippine Coast Guard for sample collection. Early reporting speeds up testing and advisory issuance. If you see unusual discoloration, foam, or fish kills in coastal waters, contact your barangay captain, municipal environment office, or the nearest Philippine Coast Guard station.
Frequently Asked Questions About Algal Blooms
Can I eat fish from waters with an algal bloom? ▾
How long do algal blooms typically last? ▾
Is it safe to swim in water with an algal bloom? ▾
Can algal blooms be prevented? ▾
What should I do if I see discolored water near my community? ▾
Algal blooms are not going away — they are likely to become more frequent as nutrient pollution and warming waters create favorable conditions. The key takeaway from the Misamis Oriental and Biliran events is that not all blooms are the same, and the appropriate response depends on knowing which species is involved. Relying on official advisories, understanding the difference between toxic and non-toxic blooms, and taking simple precautions with seafood can keep you safe while minimizing disruption to coastal livelihoods. If this was useful, you might also want to read how protecting rivers from pollution helps reduce runoff that feeds coastal blooms.
Sources
Filipino Septic Issues Cause River Pollution — Explains how untreated sewage contributes to nutrient pollution that can trigger algal blooms in coastal waters.
From Typhoons to Droughts: Extreme Weather in the Philippines — Covers how changing weather patterns influence water conditions that affect algal bloom formation.
Misamis Oriental confirms algal bloom in coastal villages. SunStar, October 2025.
Green algal bloom hits Biliran island town. Daily Tribune, March 2026.
