It's not possible to cross the toxic goop without the boat
I did the same thing as the OP, but went back (load a save point just after the bit with headcrabs and zombies, it's just outside there, on the left).
I tried and tried to get across the toxic waste, but died from it, just as the gunship appeared.
I did the same thing as the OP, but went back (load a save point just after the bit with headcrabs and zombies, it's just outside there, on the left).
I tried and tried to get across the toxic waste, but died from it, just as the gunship appeared.