Although it is named 'ZM3WaterBridge' there isn't any bridge across any water - this map is just a bridge to the water laboratory map!
To cross the lava don't walk at the wooden walkways but run and jump directly towards the waterfall. As in Ancient World there's a hot air stream (but you can't make this one visible). See there for frame rate discussions.
Behind the waterfall there's a passage at the top back wall.
Tips:Use a Search Light inside the dark rooms ;-)
To swim up the water hold your jump key and swim upwards too. There's a very strong water flow pulling you down.
Secrets:The walkway in front of the waterfall is a trap.
The ammo at the ground of the water is a trap too :-P
