Pond Scum - Definition, Glossary, Details - Oilgae
A mass of filamentous algae forming a green scum on the surface of ponds and other such bodies of water - Source
Free-floating freshwater green algae - Source
Any of various freshwater algae that form a usually greenish film on the surface of stagnant water. soruce
Links
Pond Scum Can Convert CO2 into Ethanol: [Source]
Making Biodiesel From Pond Scum