After you run through the northern sewers and get the job from the board to clean up you may run into a snag at least on ps3. For some reason after you clear the mutants it doesn't tell you the missions done. What happens is you'll start hearing a mutant and you will get hit by projectiles. I wondered why this was happening, i was not getting the mission complete pop up, at first I thought I was screwed because I couldn't finish, I spent a half hour running back and forth trying to find the invisible mutant. Finally I said I'm done and left the sewer, at that point the mission was complete.

So if you get stuck trying to find this mutant just leave and you should see the mission is done. It will not pop up but it'll be complete. Maybe this will save you some time if you run into this problem.

you get the same invisible mutie on the 360 too.. youll just see a bonestick whizzing out of a wall... no amount of grenades or rocket launcher will kill this invisible enemy but you dont need to to complete the mission.

I got this on PC in the shipyard sewers. I had an advanced sentry bot with me that the invisible (in the wall?) bonestick thrower kept aiming for.

Same thing here, on PC....

i had thata problem first run in the sewers.. not the second time when i was doing the "jobb board" misson