河川
かせん · kasen · JLPT N1 · noun
river
🌊 河 + 川: both kanji mean river, so two rivers together means rivers (かせん)
河 (usually a large river) and 川 (any river or stream) are both read kawa alone. Stacked as 河川, they give the general word for rivers.
河 — water radical 氵 + 可 (kě, phonetic)
河 is a classic semantic-phonetic compound: 氵 (water) gives the meaning 'river', while 可 supplies the sound. Originally 河 referred specifically to the Yellow River, and only later broadened to mean rivers in general.