Half-Life/Surface Tension

So we've finally reached the surface. Surface Tension is one of the largest levels in the game, both in length and sheer size. Outdoor environments have properties that allow a number of unique situations and enemies that you have not yet faced. Because some of these situations involve combat in large, complex areas, there's no one specific way to play these levels. You'll have to use your experience and creativity to analyze the particular situation that you are and play it accordingly.

The Dam
Walk through the garage door before it closes, but be wary. There is a marine to your left and one to your right, as well as several more a little farther waiting to ambush you. Using the magnum or shotgun, take out the ones right outside the entrance. Shooting the explosive barrels may take out a few of the ones farther up the canyon and save you some health and ammo. Grab the ammunition the grunts dropped and proceed with caution. Stop near the end of the tunnel where you are still somewhat protected and survey the next area from relative safety.

Here's the situation: up ahead, the road goes over a dam and ends at a closed blast door and an artillery gun emplacement. If you try to run straight across the dam, artillery fire will blow you to pieces. There is an Apache helicopter circling above that can't see you for now, but will fire at you once you are out in the open. The left side of the dam is dry, but is an unsurvivable drop. The right side, on the other hand, is full of water, but contains an Ichthyosaur (I hope you have some crossbow bolts). Every once in a while, the Apache will fire on the Ichthyosaur damaging it a little more. Technically, if you wait long enough, the Apache will kill the Ichthyosaur, but whether or not you wait for this is up to you and the supplies you have. There is a tower on the right side in the lake that has a protective alcove with a health station and a control that controls the turbine. You will need to hit this button to turn off the turbines. When you have done that, you'll have to jump into the lake and kill the Ichthyosaur. Once the Ichthyosaur is gone, swim back down to the bottom of the lake and find the valve wheel. Turning this opens the grates covering the pipes through the turbines. As long as the turbines are off, you will be able to swim through to the river on the other side of the dam. Grab the battery on the rocks and duck down underwater when the Apache is about to fire at you. Follow the river down the canyon and climb the ladder onto the structure at the end. Crawl into either pipe to escape the Apache.