South Indian River Lagoon
The 2025 health assessment for the South Indian River Lagoon is “okay” with variability across health indicators. Despite an increase in wastewater spills (82 up from 79), almost all metrics are the same in this basin between the 2024 and 2025 Report. Algae levels remain “good” and water quality is still “okay”, with a slight decrease in seagrass coverage. The only notable change was an improvement in water clarity (turbidity) across the South IRL basin.
Algal Blooms
From the chlorophyll-a data collected between August 1, 2024 to August 1, 2025, the South Indian River Lagoon experienced harmful algal bloom conditions 31.4% of the time. Of those harmful algal bloom conditions, 97.4% of blooms were considered low bloom, 2.6% of blooms were considered mid bloom, and 2.6% of blooms were considered high bloom. The median chlorophyll-a concentration in the basin for the year was 4.4 ug/L (the average concentration was 9.1ug/L), earning a “good” assessment.
Salinity
The South Indian River Lagoon had the highest median salinity of any of the five basins in 2025. While this is surprising given Lake Okeechobee discharges, it is related to the basin’s proximity to Fort Pierce, St. Lucie, and Jupiter inlets. These higher salinites are ideal for most species of seagrass in the Lagoon.
Seagrass
The South Indian River Lagoon had a “Slight Decrease” in seagrass coverage in the report period. Based on St. Johns River Water Management District satellite data, seagrass coverage declined from 8377 acres in 2021 to 7184 acres present in 2023. This represents a 14% decrease in coverage. Satellite data are taken every two years and 2025 coverage will be available by spring of 2026.
Sediment Health
Sediment health data points for the South Indian River Lagoon came from research by Florida Institute of Technology. Sediment health was too limited across the whole basin to draw conclusions with no data from the southern half of the basin. Sediment quality studies are an area where we need to expand research efforts to inform Lagoon health and restoration projects.
Wastewater Spills
Like in 2024, the South Indian River Lagoon had the largest number of reported wastewater spills. There were 82 wastewater spills that affected the South Indian River Lagoon watershed from August 2024 to August 2025. Twelve of these spills were into the Lagoon. Of those 12 spills (between 300 and 160,823 gallons), all twelve released untreated wastewater.
Water Quality
Water quality in the South Indian River Lagoon was “okay” in 2025. The health indicator assessment is based on averaging the pH, turbidity, total nitrogen, total phosphorus, dissolved oxygen, and chlorophyll-a scores in the basin. The Central Indian River Lagoon received a “good” for pH, dissolved oxygen, and chlorophyll-a concentration, “okay” for turbidity and total phosphorus, and “poor” for total nitrogen. The only change in water quality from the 2024 report was an improvement from “poor” to “okay” in turbidity (water clarity). These results are surprisingly good considering the three months of discharges from Lake Okeechobee.
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