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. Every once in a while, the Apache will fire on the Ichthyosaur damaging it a little more.
The right side, on the other hand, is full of water, but contains an Ichthyosaur (I hope you have some crossbow bolts). The left side of the dam is dry, but is an unsurvivable drop.
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. If you try to run straight across the dam, artillery fire will blow you to pieces. Here's the situation: up ahead, the road goes over a dam and ends at a closed blast door and an artillery gun emplacement. At the dam, you'll have to face a gun emplacement, an Apache, and an Ichthyosaur.
