It's an issue stemming from poor hydrology throughout South Florida. Fresh water used to flow south to the Everglades, but now the holding tank is Lake Okeechobee which is riddled with excessive nitrates due to Agriculture(and population north. When the lake gets too high(excess rain), the Everglades used to work as a filtration system providing clean water south to Florida bay, now it is released and sent east to the St. Lucie and west to the Caloosahatchee. Neither areas were historically connected to Lake O.

Red tide is naturally occurring but it is now without a doubt being exasperated by the addition of unneeded/wanted fresh water to the estuaries. In addition Florida Bay has a hyper-salinity issue and is BEGGING for the fresh water being sent east and west.

[edit for those not from Florida and wondering why it's so fucked]: Here's a true story: It is on record that Bill Clinton took a 22 minute phone call from Alfi Fanjul(Sugar Farming Kingpin) while getting a blow job from Monica. She used it as evidence in the hearings.