Charles Ellicott Commentary Jeremiah 51:36

"Therefore thus saith Jehovah: Behold, I will plead thy cause, and take vengeance for thee; and I will dry up her sea, and make her fountain dry." — Jeremiah 51:36 (ASV)

I will dry up her sea ... — The nouns mentioned here have been interpreted in various ways. Some commentators refer "her sea" to the "sea" of confluent nations and understand "her springs" to be the sources of wealth that fed Babylon's greatness. Others refer "her sea" to the Euphrates; or to the sea-like alluvial plain, intersected by canals and streams where the city stood (which was often flooded by the river, so that it became like an actual sea, as noted by Herodotus 1.184); or, specifically, to the large lake described in the note on Jeremiah 51:32.

Likewise, in Isaiah 21:1, Babylon is described as “the desert of the sea.” The Hebrew word for “springs” is in the singular, meaning her reservoir. The literal and figurative meanings probably merge, and the “drying up” describes the exhaustion of the power of which the “sea” was the symbol. In Revelation 16:12, there is apparently an allusive reference to the language of this prediction.