The term 'floating green layer' refers to a type of algae that is found in freshwater ponds and lakes. The two crossword solutions for this term are SCUM (4 letters) and PONDSCUM (8 letters). SCUM is a general term for any type of organic matter that accumulates on the surface of water, while PONDSCUM specifically refers to the type of algae that forms a floating green layer on the surface of a pond or lake.