In the Black Trench, i obtained the first key in the sewer ‘hall’, climbed back up past the whisper and unlock the door west of entance. After getting both levers pulled to access straight across i beat the elite or boss at the top of the stairs and either missed it or never got a key for the room right after the second red ‘draw’ bridge. I was able to climb up the pipes and cross them to get to the next area to the east and south of the whisper, but still havent gotten the Water Channel Key.
I also dont know if you can or now, but the foor immediately to the right of the entance that is like cell bars, i dont have a key for that neither.
TY, Awesome game!