Well you have to keep those water front properties crispy. What gets put down on grass a lot in the spring and summer? “Weed and Feed”
Algae and cyanobacteria grow rapidly when conditions align: warm water (common in Georgia summers), sunlight, and excess nutrients—especially phosphorus and nitrogen—from sources like agricultural/urban runoff, fertilizers, stormwater, septic systems, wastewater, or animal waste. Lake Lanier has a history of nutrient-driven algae issues for these reasons. 
In nature, visible blooms can form in days to weeks under ideal conditions. In optimized lab or industrial settings, certain microalgae can double in population in hours (very fast growth rates). This is why controlled cultivation works well for beneficial purposes.