I don't understand these two sentences in the article: >Natural evaporation would rapidly lower the level of the enclosed Red Sea. The dam would also lower the

I don't understand these two sentences in the article: >Natural evaporation would rapidly lower the level of the enclosed Red Sea. The dam would also lower the Red Sea by about 2.1 meters per year (6.8 feet per year). "Also?" What's the second mechanism which would the water level besides evaporation?