海藻
hǎi zǎo · HSK 7
seaweed
🌊🌿 海藻 = 海 sea + 藻 algae/water-plant = the plant that grows in the sea
海 (hǎi) is sea or ocean; 藻 (zǎo) is algae or aquatic plant, and its 艹 grass radical on top flags it as something leafy. Put the sea-plant together and you get kelp or seaweed.
海 — water radical 氵 + 每 (phonetic)
海 is a phono-semantic compound. The 氵 (water) radical signals the meaning—a vast body of water—while 每 supplies the sound. Originally referring to the sea or ocean, it later extended figuratively to mean 'vast' or 'a great quantity,' as in 人海 (a sea of people).