What manga title does this come from?

This begs for a translation, if only so we can know why the scuba gear is there.

Think it might be from this, as that was the only result on Googling "ＢＡＬＬ38苦戦".

I believe that she has been learning from a certain death note parody.
Namely: post #37147

"I leave you people alone for FIVE. FUCKING. MINUTES."

jjj14 said:
Think it might be from this, as that was the only result on Googling "ＢＡＬＬ38苦戦".

I checked and that series (Wind Mill by Hashiguchi Takashi) looks totally clean. Strange.

Casual nudity at it's most casual extreme!
- "Hey, let's go skinny dipping!"
- "B-But... we don't have a pool senpai~"
- "I know. But let's just pretend that we're on an Australian beach! It'll be a blast!"

And thus THIS happened. c.c

I've seen this picture many many times. and I JUST noticed the guy in the back has a boner.

I suspect that "BALL 38" may mean it's the 38th chapter of the manga - lots of manga have a titling convention like that, where each chapter is called "File N" or "Nth Day" or, to give more exotic examples, "Parts N" (Love and Collage) or "Nth Ball" (Oretama a.k.a. My Balls, which isn't the manga this page is from - I already checked.)

Also, I suspect from the dialogue of the girl on the far right that they actually are clothed in swimsuits, but for some reason he (and we) are seeing through the clothing. That would explain what she's referring to that she "made for use in Australia" and explain certain aspects of her pose.

UTW said:
I checked and that series (Wind Mill by Hashiguchi Takashi) looks totally clean. Strange.

It's definitely a nude filter from Wind Mill (vol. 10, ch. 38, pp. 50-51) by Hashiguchi Takashi.