St. Johns River report: salinities down after rain, algae low and manatee deaths unchanged

At its meeting, the Jacksonville Waterways Commission heard a status report on the St. Johns River from Dr. Pinto, who said recent rain has raised water levels by a couple of feet and pushed salinities lower at monitoring stations. "Our water levels are a couple of feet higher," Dr. Pinto said.

Dr. Pinto reported specific salinity readings including Mayport at 21–25 parts per thousand, Dames Point at 3–9 ppt and lower values reported near JU and downtown. Water temperatures were described as running around 69–71 °F. He said the region remains 4–5 inches below typical rainfall this time of year, with roughly 40 inches total so far and an expectation to close the year near 50–52 inches.

On algal blooms, Dr. Pinto said mixed algae have been detected at Mandarin Point, Doctor's Lake and Shands Bridge. He told the commission that toxin levels are "very, very low," with the only measurable toxin at Doctor's Lake and minor remnants of microcystis near Shands Bridge.

Dr. Pinto said there had been no change in local manatee mortalities since the previous month but noted statewide totals reported during the meeting: 89 watercraft-related manatee deaths this season out of 579 total manatee deaths in Florida. He also warned that about 68 °F is a critical threshold for cold stress in manatees and said aerial surveys had been conducted last month with another planned for next week.

Commissioners asked follow-up questions about how short cold snaps affect seawater temperature and manatee migration. In response, Dr. Pinto said manatee movement responds to both changes in daylight (photoperiod) and temperature; he added that many animals typically clear the area between mid- and late November.

The commission received the report and reserved questions for the meeting’s Q&A portion; the planned aerial survey next week was cited as the next source of updated field data.