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IRL Report Card: Mosquito Lagoon

The Mosquito Lagoon includes three management regions that have different regulatory targets. The water quality regulatory targets were established in all three areas of the Mosquito Lagoon by the St. Johns River Water Management District. Seagrass targets unique for each transect were established by St. Johns River Water Management District for the Central and South Mosquito Lagoon. Seagrass monitoring does not occur in the North Mosquito Lagoon. There are no major tributaries that enter the Mosquito Lagoon.

The Mosquito Lagoon includes:

North Mosquito Lagoon

Central Mosquito Lagoon

South Mosquito Lagoon


North Mosquito Lagoon

North Mosquito Lagoon water quality index (WQI) scores are an average of the scores for the four water quality parameters. Seagrass data were not collected in the North Mosquito Lagoon and so there is no habitat quality index (HQI) score.

Water quality in the North Mosquito Lagoon improved slightly over that past 25 years as seen in the trend graph of WQI scores over time.

Water Quality Index (WQI): Average of Chlorophyll-a, Total Nitrogen (TN), Total Phosphorus (TP) and Turbidity Scores

North Mosquito Lagoon Water Quality



Central Mosquito Lagoon

Central Mosquito Lagoon Water Quality and Habitat Quality scores plotted below show an interesting relationship. Around the year 2007, the water quality in the Central Mosquito Lagoon was very good and seagrass was starting to improve. In about 2009, this trend dramatically changed and water quality decreased. However, we don‘t see a major decrease in seagrass until 2016.

Although water quality goes up and down over the 25 year timeframe in Central Mosquito Lagoon, there is no significant change as demonstrated by the trend line. Water quality shows no change over the timeframe from 1994–2019 (25 years), however seagrass scores show a decline over that same period.

Central Mosquito Lagoon Water and Habitat Quality



South Mosquito Lagoon

Water stays in the South Mosquito Lagoon longer than almost any other part of the lagoon, in some areas the retention time is upward of a year. The south Mosquito Lagoon is also a hotspot for algae blooms to start, possibly fueled by warmer waters, high salinity, and long retention times. There is little development in the watershed of the South Mosquito Lagoon, with NASA and military campuses nearby. There is a history of citrus groves that are now abandoned but likely continue to contribute fertilizer leaching out of the soil.

Water quality scores in the South Mosquito Lagoon are overall pretty good (70 average) but in the years of algae blooms (2009, 2010, and 2016) you see a major drop in water quality driven by bad chlorophyll-a scores. Seagrass in the South Mosquito Lagoon does not go up and down with water quality like we see in the Central Mosquito Lagoon. In the South Mosquito Lagoon, seagrasses are maintaining an above average score, even with water quality deteriorating and increased herbivore pressure.

South Mosquito Lagoon Water and Habitat Quality