Research finds a connection between Caloosahatchee discharges and red tide duration

January 15, 2025
New Study Published Reinforces the Need to Reduce Lake Okeechobee Discharges to Mitigate Red Tide Blooms.

A new study published in the peer-reviewed Florida Scientist reveals important insights into the relationship between nutrient loads in southwest Florida’s coastal rivers and the duration of harmful red tide blooms.

The research, led by Sarasota Bay Estuary Program Executive Director, Dr. David Tomasko, underscores the need for targeted water-quality management, especially in reducing discharges from Lake Okeechobee to the Caloosahatchee River, which was found to play a significant role in extending the duration of red tide events.

For us, this study reinforces the importance of initiatives like LOSOM, Everglades Restoration, and the EAA Reservoir to mitigate harmful discharges and send more water south—benefiting the Everglades while protecting Florida’s coastal waters.

The Highlights

  • Nitrogen loads from the Caloosahatchee River exhibited statistically significant correlations with red tide event duration in SWFL, from Estero Bay to Charlotte Harbor to Sarasota Bay, while those from the Peace and Myakka Rivers did not.
  • Hydraulic loads (water flow volumes) from the Caloosahatchee River are as important as nitrogen content in predicting red tide duration.
  • Reducing Lake Okeechobee discharges to the Caloosahatchee River through large-scale projects like LOSOM and the EAA Reservoir can theoretically shorten red tide events in SWFL.
  • Red tides have severe environmental, public health, and economic impacts, making immediate and sustained action critical.
https://captainsforcleanwater.org/wp-content/uploads/2024/10/Photo-Mar-08-2023-12-15-01-PM.jpg

What the Study Reveals About Red Tide and Nutrient Loads

The study, titled “An Evaluation of the Relationships Between the Duration of Red Tide (Karenia brevis) Blooms and Watershed Nitrogen Loads in Southwest Florida (USA),” focuses on the impact of nitrogen loads from the Caloosahatchee, Peace, and Myakka Rivers on red tide bloom duration in coastal waters from Estero Bay to Sarasota Bay, including Charlotte Harbor.

Harmful red tide blooms (K. brevis) are an almost annual occurrence along Florida’s southwest coast and pose a significant threat to marine ecosystems, wildlife, public health, and regional economies.

They occur naturally, but previous studies have proven nutrient pollution (excess Nitrogen loads) derived from human activities—like heavily polluted Lake Okeechobee discharges—can intensify blooms by multiple factors. This latest research effort looked to build upon those previous studies and zoom in on the connection between human inputs and bloom duration.

The research team examined red tide data from National Oceanic and Atmospheric Administration (NOAA) between 2007 and 2023 alongside estimations of hydraulic and nitrogen loads to identify and correlate red tide events during that timeframe.

The findings show that the Caloosahatchee River is the primary driver of extended red tide bloom duration, establishing strong connections between the river’s nitrogen loads & flow volumes and the duration of red tide blooms. That’s really powerful data to have, albeit not too surprising considering the additional volumes of water and nutrients that the Caloosahatchee is all-too-often forced to flow during high-volume discharges from Lake Okeechobee.

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redtide_2022_grouper20
Photo Mar 08 2023, 12 17 34 PM
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redtide_2022_snook20

The study used two different definitions of a red tide “event,” based on K. brevis cell counts, and under both definitions, the Caloosahatchee River consistently showed statistically significant correlations with the length of these events.

Specifically, nitrogen loads from the Caloosahatchee (measured at the S-79 Franklin Lock & Dam) were highly predictive of bloom duration, explaining up to 77% of the variability in red tide duration.

In contrast, the Peace and Myakka Rivers—despite contributing to the overall watershed—did not exhibit statistically significant correlations with red tide bloom duration. Even when the nitrogen loads from these rivers were combined together, the results remained insignificant, underscoring that discharges from the Caloosahatchee River are a main contributor fueling these harmful blooms.

Hydraulic Loads as a Key Factor

Another crucial finding in the study was the role of hydraulic loads—the volume of water discharged—in relation to red tide duration. Interestingly, hydraulic loads from the Caloosahatchee River exhibited a similar strong predictive power as nitrogen loads.

The study found that both hydraulic and nitrogen loads from the Caloosahatchee could be used as reliable predictors of red tide duration, with more accessible data on volume flows serving as a suitable surrogate when nitrogen data isn’t available.

default

For instance, under the study’s most stringent definition of a red tide event (daily K. brevis cell counts exceeding 100,000 cells/L for 30 or more days), the hydraulic loads from the Caloosahatchee River were significantly correlated with red tide duration, accounting for 76% of the variability.

This suggests that simply reducing the volume of water discharged from the river, even without addressing nitrogen content directly, could significantly decrease the length of red tide events. Similar patterns were observed under the less stringent red tide event threshold of 10,000 cells/L.

This finding points to the importance of managing both nutrient content and water flow from the Caloosahatchee River. Reducing the flow from the river, whether through more controlled releases or storage solutions like the EAA Reservoir, could have a profound effect on mitigating harmful red tide blooms.

https://captainsforcleanwater.org/wp-content/uploads/2023/08/Member-Ad.gif

Why Red Tide is a Serious Problem for Southwest Florida

Red tides are natural, but they can be made worse by human activities. Karenia brevis, the organism responsible for red tide, produces toxins that affect marine life, causing fish kills, contaminating shellfish, and creating respiratory issues for people near the coast.

On top of the ecological and health impacts, red tide also paralyzes the economy—particularly the tourism, fishing, and real estate industries that make up the foundation of Florida’s 21st-Century economy.

An economic study that we partnered on last year found that in the event of a future Harmful Algal Bloom event like those experienced during the red-tide super blooms of 2005/6 and 2018, southwest Florida would suffer monumental economic losses to the region’s output, jobs, property values, and quality of life.

It was estimated that such water crisis events would cost over 43,000 jobs, $5.2 billion in output, and $17.8 billion in real estate value in southwest Florida alone.

The Importance of Reducing Lake Okeechobee Discharges

This study underscores the need to focus on reducing discharges from Lake Okeechobee to the Caloosahatchee River in order to shorten the duration of red tide blooms. The findings suggest that efforts to reduce those discharges through initiatives like LOSOM (Lake Okeechobee System Operating Manual) and Everglades Restoration can make a major impact.

LOSOM, which was officially implemented in August, is designed to better manage water levels in the lake, reducing harmful discharges to both the east and west coasts. The new operations plan will balance water flow, sending more water south to the Everglades where it would naturally flow instead of discarding it through the Caloosahatchee.

Additionally, advanced tools that are becoming available can leverage this new science to help maximize the flexibility of LOSOM in mitigating red tides. Tools like an early-warning forecast model for red tide created by Dr. Miles Medina of ECCO Scientific, who also co-authored this red tide duration study.

Medina’s forecast model, developed in collaboration with The Everglades Foundation, can generate weekly forecasts for red tide conditions ‘next week’ and ‘4 weeks from now’ with up to 83% accuracy. His goal is to arm the Army Corps with better data to anticipate upcoming red tide conditions more accurately, enabling more informed decision making about Lake Okeechobee releases to avoid initiating high-volume discharges into an active bloom or—just as critically—the month before an active bloom.

https://captainsforcleanwater.org/wp-content/uploads/2023/03/IMG_8125-3-e1680098236688.jpg

Even more importantly, the EAA Reservoir—a critical component of Everglades Restoration—will provide much-needed infrastructure to store, treat, and send Lake Okeechobee water south, where it belongs. You can think of the EAA Reservoir as a temporary relief drain for the Lake Okeechobee “bathtub”—allowing water managers to release water south in a more natural, controlled way and significantly reducing the need for coastal discharges.

The Road Ahead: Why Action Matters Now

By managing the flow of water and accompanying nutrients, particularly from Lake Okeechobee, we can better protect south Florida’s waters and ecosystems.

It’s not just about cleaning up after the fact; it’s about preventing these harmful events by reducing the fuel for the problem.

Advocacy for these solutions is more important now than ever, and this study provides a clear path forward for policymakers and water managers.

“Our results suggest that reducing TN loads overall—and particularly those loads originating with the Caloosahatchee River and Lake Okeechobee—may significantly reduce the duration of K. brevis blooms along the southwest coast of Florida,” concludes the study. “Understanding the numerous and evolving management objectives associated with Lake Okeechobee water levels and discharges […], the results bolster arguments for policies that are more protective of Southwest Florida coastal waters and ecosystems as an additional objective.

By reducing both nitrogen loads and water discharges from the Caloosahatchee River, we can significantly reduce the duration and intensity of red tide blooms. This will not only benefit marine ecosystems and public health but also safeguard the economic well-being of coastal communities.

At Captains For Clean Water, we believe that advocating for these science-based solutions—like LOSOM and the EAA Reservoir—is essential to preserving Florida’s waters for future generations. With your help, we can protect our waters, restore the Everglades, and ensure a healthier future for our coastlines.

New Study Published Reinforces the Need to Reduce Lake Okeechobee Discharges to Mitigate Red Tide Blooms.

A new study published in the peer-reviewed Florida Scientist reveals important insights into the relationship between nutrient loads in southwest Florida’s coastal rivers and the duration of harmful red tide blooms.

The research, led by Sarasota Bay Estuary Program Executive Director, Dr. David Tomasko, underscores the need for targeted water-quality management, especially in reducing discharges from Lake Okeechobee to the Caloosahatchee River, which was found to play a significant role in extending the duration of red tide events.

For us, this study reinforces the importance of initiatives like LOSOM, Everglades Restoration, and the EAA Reservoir to mitigate harmful discharges and send more water south—benefiting the Everglades while protecting Florida’s coastal waters.

The Highlights

  • Nitrogen loads from the Caloosahatchee River exhibited statistically significant correlations with red tide event duration in SWFL, from Estero Bay to Charlotte Harbor to Sarasota Bay, while those from the Peace and Myakka Rivers did not.
  • Hydraulic loads (water flow volumes) from the Caloosahatchee River are as important as nitrogen content in predicting red tide duration.
  • Reducing Lake Okeechobee discharges to the Caloosahatchee River through large-scale projects like LOSOM and the EAA Reservoir can theoretically shorten red tide events in SWFL.
  • Red tides have severe environmental, public health, and economic impacts, making immediate and sustained action critical.
https://captainsforcleanwater.org/wp-content/uploads/2024/10/Photo-Mar-08-2023-12-15-01-PM.jpg

What the Study Reveals About Red Tide and Nutrient Loads

The study, titled “An Evaluation of the Relationships Between the Duration of Red Tide (Karenia brevis) Blooms and Watershed Nitrogen Loads in Southwest Florida (USA),” focuses on the impact of nitrogen loads from the Caloosahatchee, Peace, and Myakka Rivers on red tide bloom duration in coastal waters from Estero Bay to Sarasota Bay, including Charlotte Harbor.

Harmful red tide blooms (K. brevis) are an almost annual occurrence along Florida’s southwest coast and pose a significant threat to marine ecosystems, wildlife, public health, and regional economies.

They occur naturally, but previous studies have proven nutrient pollution (excess Nitrogen loads) derived from human activities—like heavily polluted Lake Okeechobee discharges—can intensify blooms by multiple factors. This latest research effort looked to build upon those previous studies and zoom in on the connection between human inputs and bloom duration.

The research team examined red tide data from National Oceanic and Atmospheric Administration (NOAA) between 2007 and 2023 alongside estimations of hydraulic and nitrogen loads to identify and correlate red tide events during that timeframe.

The findings show that the Caloosahatchee River is the primary driver of extended red tide bloom duration, establishing strong connections between the river’s nitrogen loads & flow volumes and the duration of red tide blooms. That’s really powerful data to have, albeit not too surprising considering the additional volumes of water and nutrients that the Caloosahatchee is all-too-often forced to flow during high-volume discharges from Lake Okeechobee.

default
redtide_2022_grouper20
Photo Mar 08 2023, 12 17 34 PM
default
redtide_2022_snook20

The study used two different definitions of a red tide “event,” based on K. brevis cell counts, and under both definitions, the Caloosahatchee River consistently showed statistically significant correlations with the length of these events.

Specifically, nitrogen loads from the Caloosahatchee (measured at the S-79 Franklin Lock & Dam) were highly predictive of bloom duration, explaining up to 77% of the variability in red tide duration.

In contrast, the Peace and Myakka Rivers—despite contributing to the overall watershed—did not exhibit statistically significant correlations with red tide bloom duration. Even when the nitrogen loads from these rivers were combined together, the results remained insignificant, underscoring that discharges from the Caloosahatchee River are a main contributor fueling these harmful blooms.

Hydraulic Loads as a Key Factor

Another crucial finding in the study was the role of hydraulic loads—the volume of water discharged—in relation to red tide duration. Interestingly, hydraulic loads from the Caloosahatchee River exhibited a similar strong predictive power as nitrogen loads.

The study found that both hydraulic and nitrogen loads from the Caloosahatchee could be used as reliable predictors of red tide duration, with more accessible data on volume flows serving as a suitable surrogate when nitrogen data isn’t available.

default

For instance, under the study’s most stringent definition of a red tide event (daily K. brevis cell counts exceeding 100,000 cells/L for 30 or more days), the hydraulic loads from the Caloosahatchee River were significantly correlated with red tide duration, accounting for 76% of the variability.

This suggests that simply reducing the volume of water discharged from the river, even without addressing nitrogen content directly, could significantly decrease the length of red tide events. Similar patterns were observed under the less stringent red tide event threshold of 10,000 cells/L.

This finding points to the importance of managing both nutrient content and water flow from the Caloosahatchee River. Reducing the flow from the river, whether through more controlled releases or storage solutions like the EAA Reservoir, could have a profound effect on mitigating harmful red tide blooms.

https://captainsforcleanwater.org/wp-content/uploads/2023/08/Member-Ad.gif

Why Red Tide is a Serious Problem for Southwest Florida

Red tides are natural, but they can be made worse by human activities. Karenia brevis, the organism responsible for red tide, produces toxins that affect marine life, causing fish kills, contaminating shellfish, and creating respiratory issues for people near the coast.

On top of the ecological and health impacts, red tide also paralyzes the economy—particularly the tourism, fishing, and real estate industries that make up the foundation of Florida’s 21st-Century economy.

An economic study that we partnered on last year found that in the event of a future Harmful Algal Bloom event like those experienced during the red-tide super blooms of 2005/6 and 2018, southwest Florida would suffer monumental economic losses to the region’s output, jobs, property values, and quality of life.

It was estimated that such water crisis events would cost over 43,000 jobs, $5.2 billion in output, and $17.8 billion in real estate value in southwest Florida alone.

The Importance of Reducing Lake Okeechobee Discharges

This study underscores the need to focus on reducing discharges from Lake Okeechobee to the Caloosahatchee River in order to shorten the duration of red tide blooms. The findings suggest that efforts to reduce those discharges through initiatives like LOSOM (Lake Okeechobee System Operating Manual) and Everglades Restoration can make a major impact.

LOSOM, which was officially implemented in August, is designed to better manage water levels in the lake, reducing harmful discharges to both the east and west coasts. The new operations plan will balance water flow, sending more water south to the Everglades where it would naturally flow instead of discarding it through the Caloosahatchee.

Additionally, advanced tools that are becoming available can leverage this new science to help maximize the flexibility of LOSOM in mitigating red tides. Tools like an early-warning forecast model for red tide created by Dr. Miles Medina of ECCO Scientific, who also co-authored this red tide duration study.

Medina’s forecast model, developed in collaboration with The Everglades Foundation, can generate weekly forecasts for red tide conditions ‘next week’ and ‘4 weeks from now’ with up to 83% accuracy. His goal is to arm the Army Corps with better data to anticipate upcoming red tide conditions more accurately, enabling more informed decision making about Lake Okeechobee releases to avoid initiating high-volume discharges into an active bloom or—just as critically—the month before an active bloom.

https://captainsforcleanwater.org/wp-content/uploads/2023/03/IMG_8125-3-e1680098236688.jpg

Even more importantly, the EAA Reservoir—a critical component of Everglades Restoration—will provide much-needed infrastructure to store, treat, and send Lake Okeechobee water south, where it belongs. You can think of the EAA Reservoir as a temporary relief drain for the Lake Okeechobee “bathtub”—allowing water managers to release water south in a more natural, controlled way and significantly reducing the need for coastal discharges.

The Road Ahead: Why Action Matters Now

By managing the flow of water and accompanying nutrients, particularly from Lake Okeechobee, we can better protect south Florida’s waters and ecosystems.

It’s not just about cleaning up after the fact; it’s about preventing these harmful events by reducing the fuel for the problem.

Advocacy for these solutions is more important now than ever, and this study provides a clear path forward for policymakers and water managers.

“Our results suggest that reducing TN loads overall—and particularly those loads originating with the Caloosahatchee River and Lake Okeechobee—may significantly reduce the duration of K. brevis blooms along the southwest coast of Florida,” concludes the study. “Understanding the numerous and evolving management objectives associated with Lake Okeechobee water levels and discharges […], the results bolster arguments for policies that are more protective of Southwest Florida coastal waters and ecosystems as an additional objective.

By reducing both nitrogen loads and water discharges from the Caloosahatchee River, we can significantly reduce the duration and intensity of red tide blooms. This will not only benefit marine ecosystems and public health but also safeguard the economic well-being of coastal communities.

At Captains For Clean Water, we believe that advocating for these science-based solutions—like LOSOM and the EAA Reservoir—is essential to preserving Florida’s waters for future generations. With your help, we can protect our waters, restore the Everglades, and ensure a healthier future for our coastlines.