Algae, Duckweed & Sponges
Algae
Unlike marine algae, freshwater algae is usually little more than green slime. Much of it is actually microscopic single-celled organisms that form the base of the food chain. That is why the water is green ( when it is green. ) *
-- Wikipedia
* This is New Jersey ... Lord knows why the water is green. Try not to think about it.
Duckweed
You may find yourself paddling through masses of tiny green floating flecks. That is Duckweed. Duckweed is the tiniest of true plants, just a single leaf and a hair-like root.
-- Wikipedia
Sponges
Freshwater sponges are nothing to write home about. They are typically just a colorless ( or sometimes green ) mass of goo that you wouldn't want to touch, unlike marine sponges which are often big and colorful. Sponges are animals, not plants, but they act like plants, so I'm putting them here.
-- Wikipedia
