The sequence leading to a brilliant blue glow such as this is a long one starting off with a sudden influx of nutrients. Thanks to the nutrients, algae (Specifically Synechococcus Algae) start growing thriving and reproducing in droves, forming bright green patches on the surface.
The next step is for Noctiluca bacteria to come and eat the delicious algae up. This forms rust-red patches on the surface, but the spectacle really occurs at night, for the bacteria are bio-luminescent (often referred to a phosphorescent), meaning that when disturbed by a rock or boat brilliant flashes of blue appear, such as in the accompanying image. In fact all of the plants in the water glow blue at night and anyone who takes a dip in these lakes comes out glowing like radioactive waste.
Fortunately it’s harmless.