Frame rate drop on Lagoon?

For some reason on the Lagoon map, and the Lagoon map only, I get a seemingly inexplicable frame rate drop at certain times in the map. It's not consistent with particular areas either. A friend and I have the same exact setup hardware-wise and he has zero issues so I don't think it's that the graphics card can't handle it (NVIDIA GTX 770 EVGA Superclocked edition). I've made sure the drivers are updated and everything and nothing seems to fix it. 

That map and that map only is virtually unplayable because of it, but every other map runs perfectly smooth. 

Any explanation?