Town staff: collapsing algal bloom and low oxygen likely behind Buccaneer Lagoon fish kills; education planned

Town staff told the Murph (Marine and Environmental Resources Task Force) advisory committee on April 8 that preliminary water samples from Buccaneer Lagoon show signs consistent with a collapsing harmful algal bloom and that extremely low dissolved oxygen levels likely contributed to the recent fish kills.

"Water temperature, salinity, and pH were all within normal ranges," said the staff member reporting the tests, "but dissolved oxygen was extremely low, ranging from 0.03 to 3.35 milligrams per liter." The staff member said laboratory analysis identified high concentrations of algal cells — notably raphidophytes and Heterocapsa species — at levels orders of magnitude above typical background counts.

The staff member described the bloom as "collapsing," leaving silicate cell walls suspended in the water column that produced a pale, chalky discoloration. That decomposition, the staff member said, would account for oxygen depletion and the odors produced by anaerobic bacteria.

Town staff credited FGCU and Florida Fish and Wildlife (FWC) partners for helping collect and analyze samples and said they have shipped additional samples to FWC for further testing. The committee heard that a separate fish kill on the 7000 block — dozens of mostly redfish and mullet — is under parallel analysis; an initial field reading there showed temperature near 27°C and elevated chlorophyll (roughly 67 compared with a typical reading near 5).

While staff noted natural blooms can occur, they stressed that nutrient inputs such as fertilizer can exacerbate eutrophic events. "We're working on some educational materials to send both to the houses and for the condo owners," the staff member said, adding that staff met with condominium managers, waterside association representatives and landscapers to review best practices and the town's fertilizer ordinance.

Committee members asked staff to follow up once more data are available and to return recommended outreach materials to the committee. Staff suggested planting native species in runoff-prone areas, reinforcing the fertilizer ordinance and using PIO channels and photos to raise awareness. Staff also cautioned that, in a first-flush event after long drought conditions, even full compliance with a fertilizer ban might not entirely prevent a bloom if material accumulated over time is suddenly washed into the lagoon.

Next steps: staff will report back as FWC analysis is completed and will circulate proposed outreach materials and recommended practices for condominium and homeowner audiences.