Where is the Ancient Waterway in the Dahlgur Oasis?

I'm in the Dahlgur Oasis and have to find the Ancient Waterway. I had previously explored the entire map, but I don't see where I should be going.

Any suggestions for where I should be looking for it?

On your map, it's just northwest of the Healing Well. There's a little indentation in that area you haven't explored. Look for a bridge, guarded by a yellow-named monster.

Note the pattern (from left to right) of the three rocks, the small upwards indentation, and then the second small upwards indentation. That should allow you to align my map with yours.

The entrance to the Ancient Waterway is a thin bridge off the edge of the map, typically in the north. Its passage is blocked until you're up to the appropriate quest level, but I assume you're there if you're asking this question.

On your map I see a number of places where you haven't explored to the very edge of the map - I would suggest running around the very edge of the map, starting with the northern edge. You should be able to find it.