Climb the Chain to Escape the Monster in 80s Horror

by Dan
(Maryland)

I'm looking for the title of a horror movie that I only remember bit's and pieces of.

I think the opening part of the movie shows the town's water supply being contaminated somehow, which eventually produces a mutated monster.

The only other scene I remember, as a kid, gave me nightmares for awhile. It was of this guy trying to escape the monster. He was in a warehouse, being chased. His only escape was by climbing this rope/chain/similar. The monster kept closing in as he struggled up. He finally managed to get to the top of the warehouse as dawn was breaking.

Sorry for not providing more details. Could probably fit any 10 movie plots :) Does anyone have any ideas?