Lyngbya sp.

Source of the photo: 
http://silicasecchidisk.conncoll.edu/Pics/Other%20Algae/Blue_Green%20jpegs/Lyngbya_Key223.jpg
Author of the description: 
KÖRINFO
Lyngbya sp.

Micrscopic view of a Lyngbya species with higher magnification.