North Indian River Lagoon
The 2025 health assessment for the North Indian River Lagoon is “okay”. All three metrics that contribute to the overall assessment (harmful algal blooms, seagrass coverage, and water quality) remained the same between 2024 and 2025. Algae levels and water quality were “okay” with a fewer number of wastewater spills. Seagrass coverage continued to increase and the only notable water quality change was a slight dip in basin-wide dissolved oxygen median values.
Algal Blooms
Chlorophyll-a data collected between August 1, 2024 to August 1, 2025 show the North Indian River Lagoon experienced harmful algal bloom conditions 62% of the time. Of those harmful algal bloom conditions, 57.7% of blooms were considered low bloom, 17.6% of blooms were considered mid bloom, and 24.7% of blooms were considered high bloom. The median chlorophyll-a concentration in the basin for the year was 6.98 ug/L (the average concentration was 12.9 ug/L), earning an “okay” for the year.
Salinity
The Northern Indian River Lagoon Basin has the lowest median salinity of all five basins. Like Mosquito Lagoon, this basin has a long residence time (meaning the water stays there for a long time). However, this area receives a lot of freshwater runoff from stormwater, driving down overall salinity. Much of the seagrass regrowth in the North IRL is Widgeon Grass (Ruppia maritima), which prefers fresher waters. Although the salinity is in the preferred range for red mangroves, the Northern IRL represents the northern boundary of the species due to temperature preference, so black mangroves are more prevalent in many areas.
Seagrass
The North Indian River Lagoon saw a large increase in seagrass coverage in this year’s Report based on the most up-to-date data. Based on St. Johns River Water Management District satellite data, seagrass coverage changed from 66 acres in 2021 to 580 acres present in 2023. Although seagrass coverage isn’t near peak coverage, there was a 777.8% increase 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 North Indian River Lagoon came from research by Florida Institute of Technology. Although the number of datapoints in the basin increased from 0 to 21, sediment health is still too limited across the whole basin to draw meaningful conclusions. However, available sediment data indicate good overall soil health, which is good news for potential seagrass growth.
Wastewater Spills
From August 2024 to August 2025, there were 18 wastewater spills that affected the North Indian River Lagoon watershed with seven releasing into the Lagoon. Of those seven spills (between 10 and 60,000 gallons), three released untreated wastewater, three released reuse water, and one released treated wastewater.
Water Quality
Water quality in the North Indian River Lagoon was consistent between 2024 and 2025, assessed as “okay” in both years. 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 North Indian River Lagoon received a “good” for pH, an “okay” for turbidity, total phosphorus, dissolved oxygen, and chlorophyll-a concentration, and a “very poor” for total nitrogen. The only change in 2025 was a slight drop in dissolved oxygen levels, though not significant enough to drive any fish kill events.
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