also: すいそう
noun
water plant; aquatic plant; waterweed
General term for plants that grow in water, including both freshwater and marine species.
池に水草がたくさん生えている。
A lot of water plants are growing in the pond.
水草は水質を浄化する役割がある。
Water plants play a role in purifying water quality.
海藻 specifically refers to marine algae or seaweed, while 水草 is a broader term for any aquatic plant.
Compound of 水 (water) and 草 (grass, plant). The reading みずくさ is the native Japanese reading (kun'yomi), while すいそう is the Sino-Japanese reading (on'yomi).