The authors study three samples from French Guiana. They describe 260 freshwater algae taxa (excluding Diatomophyceae). Desmidiales are predominant with 78 %.The algae from tropical or subtropical lands represent nearly half of the florula (47 %). Among the typical algae nearly 50 % are only known from America. This acidwater florula is very similar to the brazilian one, peculiarly to this from Amazonia. Sixteen new species, varieties and formae in the genera Anabaena, Closterium, Actinotaenium, Cosmarium, Cosmoclodium, Staurodesmus, Staurastrum and Groenbladia are proposed