Half-Life 2 Walkthrough -> Radioactive Waters
We head to the old red hangar. But a headcrab rocket has already crashed there, turning the people into zombies. There's some health in a cage above the water—to reset it, you need to go up to the attic and knock out the barrel holding the mechanism:
Further along the canal, you'll come across a bridge where a man will drop off some health. Beyond the bridge is a ramp that needs to be raised. Climb into the pipe and emerge above a square pool.
Breaking Through the Broken Gates
Navigating through the canals isn't particularly difficult. The main dangers are the Lizards hanging from some of the spans and the harvesters firing from the banks. When we reach the closed gates, we need to disembark at the canal's bend. There, we climb the stairs and navigate through the rooms until we reach the gates.
Escape from the Stormtrooper
The next gate will close in front of us. It'll be in the area where the containers are parked on the shore and a helicopter flies over the water. Note the turret on the corner next to the gate – it's where the switch that opens it is. Swim to the pier in the "grotto." There, we knock the lock off the door and, finding a magnum, exit to the containers.
Avoiding the firing helicopter and fighting the Combines, we make our way between the containers to the building labeled "Equipment." There, we climb onto the balcony along the perimeter and then, passing through the building, we emerge back onto the street, where the tower is just a stone's throw away.
To raise another ramp we encounter, we need to drop the washing machine on top of the descending cage. Go back a bit – there will be a ladder leading up between two concrete pipe blocks. There you need to walk along the walkway to the balcony and throw the washing machine from there – the ramp will rise:
Next, rebels are waiting for us in the tunnel. We go out to the shore to join them. We talk to the man. We go into the room. He tells us that Eli is waiting for us on the dam. Meanwhile, a Vortigaunt welds a machine gun to the boat.
We emerge into a small body of water with islands. Here, a big battle with a helicopter awaits us. We shoot it down with our cannon. The boxes on the islands contain some health and armor. It's best not to attack head-on, but to fire at the helicopter from the sides and below.
After killing him, drive through the gate marked "Port 5." Leave the boat there and head to the building with a large health pod. After passing the building, walk along the walkway to the dam. Turn the lever to open the gate. Return to the boat and jump through the gate from the ramp.
Afterward, you'll be introduced to the "Eastern Black Rock" laboratory (Black Mesa).