Blue green algae is otherwise called cyanobacteria (bacterial classification- prokaryote), green algae is eukaryotic. The pigment present in blue green algae is phycocyanin and chlorophyll in case of green algae Blue green algaes kingdom is moneran and green algae is not moneran.
Nutrient-rich lakes or ponds may support rapid growth of blue-green algae (algae blooms). Blue-green algae are actually bacteria. They are called cyanobacteria after the blue-green pigments that they produce.
Bacteria and blue-green algae are both primitive prokaryotes that live on earth now, as well as long time ago. Just recently they have changed blue green algae or cyanobacteria to be in the kingdom prokaryotes.
The taxonomy of blue-green algae is in transition, this means it can being dealt in botanical nomenclature code or bacteriological nomenclature code. They seem to have the characters of algae and bacteria respectively.