Toxic Algae Bloom Plagues Caloosahatchee River in Southwest Florida

Experts link drought and pollution to the spread of dangerous blue-green algae along the 45-mile waterway.

Published on Feb. 18, 2026

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A massive algae bloom has stretched for miles along Florida's Caloosahatchee River, raising concerns among experts and advocates. The bloom, identified as a species that can produce dangerous toxins, is likely fueled by the current drought creating stagnant, warm water conditions ideal for algae growth. Advocates argue that excess nutrient pollution is the root cause and the state must do more to prevent it.

Why it matters

The Caloosahatchee River is a vital waterway in Southwest Florida, providing drinking water, recreational opportunities, and supporting the local ecosystem. Toxic algae blooms can pose serious health risks to humans and wildlife, and have been linked to neurodegenerative diseases. Addressing the underlying causes of these blooms, such as nutrient pollution, is crucial to protecting the region's environment and public health.

The details

Experts from Florida Gulf Coast University have identified the algae as Microcystis flos-aquae, a species that can produce toxins causing liver damage, tumor formation, and potentially contributing to diseases like Parkinson's and ALS. The bloom stretches for miles, clouding the shoreline, canals, and oxbows. While a dry-season bloom is less common, the drought has created the ideal stagnant, warm conditions for the algae to thrive. Advocates argue that excess nutrient pollution, likely from agricultural and urban runoff, is the root cause that the state must address to prevent future blooms.

  • The algae bloom was first observed in mid-February 2026.
  • Pilot Ralph Arwood photographed the extensive bloom on February 21, 2026.

The players

Mike Parsons

Professor of Marine Science at Florida Gulf Coast University's Water School, who believes the drought-created stagnant water conditions are the likely cause of the algae bloom.

Barry Rosen

An algae expert at Florida Gulf Coast University, who identified the bloom as the species Microcystis flos-aquae, which can produce dangerous toxins.

Jason Pim

A board member of the Calusa Waterkeeper organization, who argues that the state must do more to stop nutrient pollution from entering the waterways and fueling these harmful algal blooms.

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What they’re saying

“Blue-green algae tends to prefer 'aged water' that has been sitting around for a while. As the waters warm, the cyanobacteria (blue-green algae) will have higher metabolic rates which may lead to more growth and a bloom.”

— Mike Parsons, Professor of Marine Science (naplesnews.com)

“The question really is: Is this particular organism transient? Obviously it has the right nutrients, the right light intensity and the temperature's right ... what's next? Will there be something else waiting in the wings to take over? Will this one peter out?”

— Barry Rosen, Algae Expert (naplesnews.com)

“The state must do more to stop nutrient pollution before it enters the water. Trying to address it after the fact takes exponentially more effort and (taxpayer) money.”

— Jason Pim, Calusa Waterkeeper Board Member (naplesnews.com)

What’s next

The Florida Department of Environmental Protection plans to sample the bloom to determine the specific species and whether it is producing toxins. Authorities will also monitor the situation and take action if the bloom poses a threat to public health or the environment.

The takeaway

This algae bloom highlights the urgent need for the state of Florida to address the root causes of nutrient pollution that fuel these harmful events. Proactive measures to reduce agricultural and urban runoff are crucial to preventing future toxic blooms and protecting the Caloosahatchee River ecosystem and the communities that depend on it.