noun
freshwater algae
General term for algae living in fresh water, as opposed to marine algae.
この池には淡水藻がたくさん生えている。
A lot of freshwater algae grow in this pond.
海藻 refers to marine algae (seaweed), while 淡水藻 specifically means freshwater algae.
Compound of 淡水 (fresh water) and 藻 (algae).