tidemark
/ˈtaɪdmɑːk/noun
1- a mark left or reached by the sea on a shore at the highest point of a tide潮痕, 潮标（海潮达到的最高点）。
1.1
- Brit. a mark left on a surface, especially around the inside of a bath or washbasin, at the level reached by water〈英〉（尤指浴缸、脸盆的）水（垢）痕。