Stuck in Alyx's "Nasty Water" section

[TaoFan]

This is the bit straight after what seems to be the underground carpark section, where you plug the antlion holes with car wrecks.

I and Alex go down some steps, only to emerge in a flooded area, with no idea what to do next. How do we proceed from here?

 

[Roland Deschain]

Screens always help.

Did you go all the way down the stairs. If yes, its a dead end with a supply crate. Go up a couple of floors and you'll see another exit that leads to another flooded area where you can proceed.

 

[Asus]

Have you gone around fences in the flooded room to the other side where the stairs are?

 

[hasan]

IIRC
There is an exit leading to stairs and a dead end. There's another exit leading to a room with fences and a couple of zombies .. just go around the fences and you'll see the next place.