1. Keep an eye out for this ladder which will be on your right. Exit your boat and climb above to grab the supplies from the catwalk.
2. If you look closely you can see G-Man standing on these docks. Pull up and defeat the zombies and head crabs inside. (You'll find steps then a ladder on the right.)
3. Knock this barrel aside with your crowbar to let loose the goodies ahead. Jump into the water to retrieve them.
4. Jump back on your fan boat and speed over this convenient ramp.
5. This nice man tosses you some supplies. You can just drive right over the supplies to pick them up.
6. Exit your boat, noticing the teetering ramp ahead. Climb into the opening at (1) to push the barrels from the exit at (2).
7. Grab the barrels and carry them underwater, releasing them into this catch basket. You'll need at least 3 barrels to life the ramp into place and there's already one in there when you arrive.
8. The ramp lifts into place, allowing you to jump over the wall ahead.
9. Press on, running over supply crates (and CPs) as you advance. You'll know you're getting close to the next area when you spot a water tower. Note the pipe-tunnel with its grate lying next to it. HazardousExecutioner suggests that you take the barrel, and place it at the mouth of the tunnel. Then hop in for a swim and some good stuff.
10. Shortly thereafter you'll spot this guy shooting at you from above. Swing around behind him to the right.
11. Exit the boat and take him out. Climb the stairs and find a ladder to the left. Enter through the door above.
12. Search the two rooms to the left for supplies. To the right are these CPs. Continue through a door just left of the explosion seen here.
13. A swarm of Manhacks breaks through these windows. A lone CP can be seen ahead. A medical station is behind him.
14. Don't miss this supply crate before heading through the door on the right.
15. A solitary CP gunner is barricaded ahead. I got lucky with a grenade once but found rushing him with the SMG to be the most consistent tactic for taking him out. Grab energy from the blue dumpster far-right before proceeding through the door on the left.
16. Three CPs wait in ambush. Stay in the doorway and chip away at them. Supplies are on the table ahead and the crate behind it. Note the medical station on the wall.
17. A single shell for your SMG's grenade launcher can be found atop this generator. Continue up the stairs and through the door on the right.
18. The gate controls are broken (inset). Shoot the explosive barrels on the right, sending these beams swinging toward the large doors.
19. The beams smash open the gate. Shortly after, this Combine dropship whizzes past.
20. Start backtracking to your boat and find that more CP troops have arrived. Mow them down with the gun turret you passed earlier.
21. Grenades are your friend in the garage, especially against the gunner farther to the right.
22. Hop back into your fan boat and sail through the now-open gate, making sure to retrieve supplies from the two crates just visible ahead.
23. This next segment is a lot of fun. Push it to the max and grab some big air as seen here. Rockets are being fired at you from the truck in the distance so keep moving.
24. CPs rappel from the overpasses above -- no time to slow down!
25. When you get to this fire barrier keep right and ramp over the obstacle through the tunnel ahead.
26. The sequence climaxes with multiple explosions sending vehicles flying as you hurl past. Either tunnel ahead will do, just keep moving to load the next area.
27. Keep right then exit the boat when you spot this Lambda. Remove the cinder blocks from the basket on the right and the basket above will lower so you can grab the supplies.
28. Farther on an alarm sounds as gate #5 closes. Take out the CP visible here then continue on your boat to the right.
29. Dismount your boat and enter the building by shooting the lock on that door ahead.
30. Grab the .357 Magnum and supplies from the table. CPs enter through the door, but your .357 will take each out with a single shot. Note the supply crates ahead.
31. Ready your .357 and head up these stairs. A chopper is circling so move fast. Drop the CP above then continue between the shipping containers straight ahead and slightly to the left.
32. Continue through the maze of shipping containers and into this one. Notice the two supply crates inside.
33. Turn left into the building. Rush into the indicated container for cover from the many CPs in this area. Inside you'll find health and energy. Hang out here for a while and let the CPs and Manhacks come to you.
34. This next part is very difficult so make sure you save your game first. Exit the shipping container out the far side and rush up the stairs to your right. More CP troops come in the front door -- toss a grenade their way then slip back into the shipping container.
35. Take pot shots at the reinforcements with your SMG, tossing the occasional grenade when they get bunched up.
36. Once quiet, return up the stairs then hop across the tops of the containers to the other side.
37. Move fast to avoid the chopper fire as you bust through these crates to the doorway.
38. More CP are on the stairs beyond (inset). Mercifully, these health and energy stations are at the bottom of the stairs. Two supply crates are behind you. If you exit the door seen here and keep right, you'll come to a supply crate with health inside.
39. If instead you go straight on, you'll come to these stairs (inset). Take them down then turn right to this ladder. Toss a grenade to the boys above before climbing.
40. Man the left turret and pummel the chopper. It will move position right in front of the other turret. Rinse and repeat to send it limping away.
41. Press the big red button to open gate #5, visible through the window.