high-water mark
/ˈhaɪˈwɔːtə(r)/noun
1- the level reached by the sea at high tide, or by a lake or river in time of flood（海水的）高潮线, （发洪水时河湖的）高水位线。
1.1
- a maximum recorded level or value最高纪录, 最高水平, 最大值：
unemployment and crime both stand at a high-water mark.
失业率和犯罪率都达到最高纪录。