Hundreds of sea turtles have washed up on Southwest Florida beaches — including 17 in the past week alone — in a “mass mortality event” that far surpasses the usual yearly numbers, according to a new report.

The deaths — which experts suspect may be caused by the red tide bloom in the area — will impact the recovery of the turtles, a protected species, The News-Press reported.

The most recent carcasses have been recovered from Sanibel and Captiva waters, according to the report.

“Our average for the entire year is usually around 30 or 35, but we’ve had 53 in June and July alone,” Kelly Sloan, a sea turtle researcher at the Sanibel-Captiva Conservation Foundation on Sanibel, told the paper.

“Most of [the turtles] have been mature adults, and only 1 in 1,000 make it to adulthood,” she added. “It takes a loggerhead 25 to 30 years to mature, so that really does have a significant impact on their recovery.”

Sloan’s organization has picked up 91 sea turtles on the islands since the red tide bloom — an overgrowth of algae colonies — began in October, she said.

Algae blooms run like a ribbon along coast lines, producing toxins and turning the affected water red. While sea turtles are often able to detect the algae and avoid areas with a high concentration, the toxins remain in the marine environment for months, according to the organization Sea Turtle Inc.

Large marine animals that eat small fish contaminated by the toxin can become ill and even die, according to AccuWeather. Beachgoers in red tide areas might develop a cough or watery eyes.

Though Sloan called this year’s red tide event the “longest continued bloom since 2006,” researchers couldn’t say for sure whether it directly caused the deaths.

The red tide bloom has varied in intensity and distribution, sometimes stretching from Tampa Bay to the Florida Keys, according to The News-Press.

Although blooms usually begin in Sarasota, this one is centered in northern Lee, the paper reported.

The organism responsible for red tide — Karenia brevis — occurs naturally, but the blooms can be intensified and lengthened as a result of farming and development, water quality researchers told the paper. It contains brevetoxin, which affects fish nerves and gills — causing them to die, Dr. Richard Stumpf, oceanographer for National Oceanic and Atmospheric Administration’s National Centers for Coastal Ocean Science, told Accuweather.

Katerina brevis is always present at low concentrations in the Gulf of Mexico — but if it reaches an area with more nutrients when the water is relatively calm, it grows, according to Stumpf.

“In the fall, changes in the wind patterns create upwelling on the Florida coast that, when combined with the swimming, accumulates Karenia at the coast,” he said.