Albert Barnes Commentary Jeremiah 48:34

"From the cry of Heshbon even unto Elealeh, even unto Jahaz have they uttered their voice, from Zoar even unto Horonaim, to Eglath-shelishiyah: for the waters of Nimrim also shall become desolate." — Jeremiah 48:34 (ASV)

The meaning is that, taking up the lamentation of Heshbon, the Moabites break forth into a wail, heard as far as Elealeh, scarcely two miles distant (Numbers 32:37), but from there spreading over the land to towns on the southern and southwestern borders of the land.

An heifer of three years old - Applied in Isaiah 15:5 to Zoar, but here to Horonaim. Some take “an heifer” as a proper name, and render it: “Eglah for the third part” . Zoar, Horonaim, and Eglah formed a tripolis, or confederacy of three towns, and Eglah might therefore be put after either one or the other.

Nimrim - Probably the Wady-en-Nemeirah at the southeastern end of the Dead Sea.