Half life 2 question

[amdwolfman64]

So now i'm at this dam. What do I do to get over this dam. OR open it and.

 

[royaldank]

gamefaqs.com

Sounds like the part where you have to go through the building, out onto a ledge, and then turn right to shoot some barrels that releases a battering ram of sorts.

 

[DerKaiser]

If you're facing the dam, have you entered the building up and to your left? You need to go up there, kill the guys and walk over to the dam and turn a wheel and open something. Then you can run your boat up on some logs at full speed and through the dam.

Sorry, I just remembered there is more than one dam. The dam I'm thinking about above is after you down a helicopter or two.

There's a really good walkthrough here.