Here is a news bulletin from the Springdale Estates Lake Committee

This month, as is typical this time of year, floating blobs with an odd green color have shown up on Lower Springdale Lake.  The color looks 'man-made' as if paint were spilled into the Lake.  However, the blobs are natural - they are a blue-green algal bloom.
The organism forming the floating green blobs is Planktothrix (formerly known as Oscillatoria), probably the species Planktothrix agardii.   Many thanks to Mark Vander Borgh of NCDENR for confirming the identification.  A whole host of fascinating microscopic organisms live in these blobs so if you have a microscope, check them out!  Anabaena, another blue-green algae, is also actively growing in Lower Springdale Lake.
Blue-green algae (also known as cyanobacteria - they are a type of bacteria and are not 'true' algae) including Anabeana and Planktothrix can produce microcystins which can cause liver toxicity if ingested.  Although to date there have not been any adverse human heath effects attributable to blue-green algae in North Carolina according to the NC Division of Water Resources, it would still be prudent not to swim in the Lake or to allow dogs to swim in the Lake until the bloom passes.  

With global warming, blue green algal blooms are expected to increase.  In August 2014 Toledo Ohio had to issue an advisory not to drink the tap water because of microcystin contamination from a blue-green algal bloom in Lake Erie.

Van Cotter for the Springdale Estates Lake Committee