South Indian River Lagoon
The 2026 health assessment for the South Indian River Lagoon is “Large Improvement.” This is a step up from the “Slight Improvement / Stable” reported in 2025. Notable changes include a slight increase in seagrass coverage and improved overall water quality. It should also be noted that there were no discharges from Lake Okeechobee in the reporting period.
Algal Blooms
From the chlorophyll-a data collected between August 1, 2025 to August 1, 2026, the South Indian River Lagoon experienced algal bloom conditions 2.40% of the time and never reached mid or high bloom conditions. The median chlorophyll-a concentration in the basin for the year was 3.62 µg/L, earning a “good” assessment congruent with lower nutrient concentrations.
Salinity
The South Indian River Lagoon had the highest median salinity of any of the five basins in 2026 (median= 33 ppt). These higher salinities are ideal for most species of seagrass in the Lagoon and are related to lower residency time of water in the Lagoon (more more interchange with the ocean).
Seagrass
The South Indian River Lagoon had a “slight increase” in seagrass coverage in the report period. Based on St. Johns River Water Management District mapping data, seagrass coverage increased from 7,184 acres in 2023 to 9,132 acres present in 2025. This represents a 21.33% increase in coverage. The South IRL basin showed slight decreases in coverage during previous reporting periods. Mapping data are taken every two years and 2027 coverage will be available by spring of 2028.
Sediment Health
Sediment health data points for the South Indian River Lagoon came from MRC, Florida Institute of Technology, and Smithsonian Fort Pierce Marine Station research. 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 2025, the South Indian River Lagoon had the largest number of reported wastewater spills. There were 75 wastewater spills that affected the South Indian River Lagoon watershed from August 2025 to August 2026. Five of these spills were into the Lagoon. Of those five spills, all five released a total of 34,450 gallons of untreated wastewater.
Water Quality
Water quality in the South Indian River Lagoon was “good” in 2026—an improvement from the “fair” assessment 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. Decreased nitrogen concentrations are the biggest contributor to the improved water quality this year.
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