In reality, sea level varies according to the irregular interior of the planet.

事实上，海平面会根据地球不规则的内部而变化。

youdao

"If we find a mine, we inform the national authority, and we would re-route the pipeline, " he explains, adding that the real challenge is the length of the pipeline, the shallow nature of the Baltic Sea and the irregular seabed.

BBC: RELATED BBC SITES