Pop 5000 Balloons with Portable Lake Pros

[battlezoby]

I have the "It came from below" challenge which says:"Pop 5000 Balloons with Portable Lake Pros" as a daily challenge, but can't seem to figure out what it means.

I had hoped it meant pop 5000 balloons using anything mount on a portable lake, but popping a whole mess of balloons via a Buckaneer and Submarine in a portable lake didn't even show up as a partial completion. (Update: I tried both versions of fully upgraded sub too, but not the upgraded lake ability like Little Nemo suggested below.)

Is it completely broken, or is there something else you're supposed to do to satisfy the challenge?

[Little Nemo]

If I remember correctly the Portable Lake Pro (but not the non-Pro version) has an activated ability that upon using it some tentacles appear and destroy bloons. Perhaps it is what that challenge meant.

[battlezoby]

Thanks. Took almost $2,000 of in-game money to buy enough pools to upgrade to Pro, but then I managed to pop 5000 balloons that same game. (Spoiler) I just placed a few at the beginning of the maze, along with a bunch of 2-upgrades-each-path Chippers and bunch of Apprentice Money Tornados to keep the smaller-than-MOAB balloons on that half of the screen. Anything that got further first fell into range of the "big guys" like Super Monkeys and the like. I had to go into "overtime" (Freeplay) before I got 5000, but I did.