This quest was marked obsolete by Blizzard and cannot be obtained or completed.
Ysiel Windsinger wants you to look for signs of Cenarion Expedition Druids near the entrance to Coilfang Reservoir in Zangarmarsh.
I sent a small group of our druids to investigate the drain you discovered inside of Serpent Lake. They were expected to return shortly after. Needless to say, they did not.
You are amongst our most capable allies; I ask you to seek them and find out what became of them.