When 5 players have pulled the levers at the same time in The Ringing Deeps, a zone-wide announcement goes out with the text As the earthen machinery turns, something begins to stir in the nearby lake.
This precedes the spawning of the "Lurker of the Deeps" rare by about a minute (haven't actually timed it)

If SilverDragon could give an alert when it detects that announcement that would be great, as otherwise you're probably going to be too late.