Took a walk in a storm drain near my house this sunny afternoon. During heavy rain this fills up with rainwater but it's been quite dry recently.
This is how I got down to the bottom of the drain.
Underpass where the road runs over the drain. The smell got worse as I walked towards this, probably due to a number of big pipes with effluent trickling out:
On the wall of the underpass tunnel.
Gunk blocking up some of the discharge pipes.