The Ruins of Eldre'thar are newly discovered ruins of a Highborne city located inside Sishir Canyon. The ghostly highborne elves still haunt the area. The area is a night elf archaeology dig site and Nal'taszar can be found floating the lake's waters. Various conversations can be overheard among the named highborne ghosts.
This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore.
Maybe something similar as in  Forgotten Rituals at Lake Elrendar has happended to the citizens, as Highborne Sorcerers are seen channeling at the lake shores.