The underground waterway is a small passage composed with light up the ceiling and filled with sewer water. The passage appears to be linking the Cesspool Entrance and the Kennel room.
Resident Evil 2
For both scenario A and B for Leon or Claire, two web spinner are present as enemies in the passage. Because the passage is very narrow, dodging the poison spit from the web spinner can be very difficult.
Resident Evil: The Darkside Chronicles
The Sewer Manager's Diary file is in this room, when turning around the first corner, shoot the light on the ceiling furthest back.
There are a total of 9 main enemies in this area, plus the many baby spiders. A grenade will clear all small spiders in one hit on all difficulties.