Phytoplankton
From LGPedia
"Phytoplankton are the autotrophic component of the plankton that drift in the water column. The name comes from the Greek terms, phyton or "plant" and πλαγκτος ("planktos"), meaning "wanderer" or "drifter" (Thurman, 1997). Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, they may appear as a green discoloration of the water due to the presence of chlorophyll within their cells (although the actual color may vary with the species of phytoplankton present)." - Wikipedia
Video Where Strange Tag Appears
Speculation
May refer to the red sea which is colored by phytoplankton although this conclusion is reached via Cassieiswatching clues.
