Filamentous Green Algae (spp. in Chlorophyta and Charophyta families) 2016-2-24 Bombay Hook NWR, DE

This might look like it's floating on the water, however, it is totally submerged.
Filamentous is the most common type of Green Algae.
http://mdc.mo.gov/discover-nature/field-guide/filamentous-green-algae-moss-pond-scum
"it feeds and shelters tiny animals, insects, and young fish" and "is vital for healthy aquatic ecosystems"
http://aquaplant.tamu.edu/plant-identification/alphabetical-index/filamentous-algae/