This is incredibly fun and addictive. I honestly couldn't pull myself away from the game to rate it (until Steve scammed me at the end). Great work!
One slight issue is that I'm not really sure what the defenses/knifes do. I know they're supposed to defend divers from sharks, but it didn't look like the sharks actually did anything when they hit a diver. That said, I could have easily missed it, since my strategy was to just spam divers to the point where it was hard to keep track of a single one.