also: そうずがわ
noun
Sanzu River; River of Three Crossings
In Japanese Buddhism, the river that the dead must cross; often compared to the River Styx. The reading さんずがわ is standard, while そうずがわ is rare.
See also: 三途の川
三途川を渡るとき、故人は六文銭を渡すと言われる。
It is said that when crossing the Sanzu River, the deceased pays six mon coins.
あの世とこの世の境には三途川が流れていると信じられている。
It is believed that the Sanzu River flows between this world and the next.
Same meaning; 三途の川 is a slightly longer, more explanatory phrase, while 三途川 is a compound noun.
From Buddhist terminology; 三途 (sanzu, 'three ways') refers to the three crossings of the river based on one's deeds, and 川 (kawa, 'river'). The reading そうずがわ is a rare variant.