Jamieson, Fausset and Brown on Jeremiah 51:13

13. waters--(Jr 51:32, 36; see on Is 21:1). The Euphrates surrounded the city and, being divided into many channels, formed islands. Compare as to spiritual Babylon "waters," that is, "many peoples," Re 17:1, 15. A large lake also was near Babylon.

measure--literally, "cubit," which was the most common measure, and therefore is used for a measure in general. The time for putting a limit to thy covetousness [Gesenius]. There is no "and" in the Hebrew: translate, "thine end, the retribution for thy covetousness" [Grotius]. Maurer takes the image to be from weaving: "the cubit where thou art to be cut off"; for the web is cut off, when the required number of cubits is completed (Is 38:12).