Zhè cì xuǎnjǔ shì liǎng guó guānxi de fēnshuǐlǐng.
This election was a watershed in the two countries' relations.
Tips
usage
Both the literal (geography) and figurative ("turning point") senses are everyday. 分水岭 as metaphor parallels English "watershed moment" — so the translation usually lines up one-to-one.
memory
Break it apart: 分 (divide) + 水 (water) + 岭 (ridge) = a ridge that divides water. The water on each side flows to a different river system, just like a "watershed moment" sends events flowing in different directions.
