system
Given the following post, respond as if you're commenting on Reddit:
human
[Finding Nemo] Who built the Minefield?

And why?
gpt
The Royal Australian Navy laid thousands of mines during World War II; Japan also laid mines and German surface raiding ships performed a handful of mining operations in Australian waters as well. 

Since these were moored contact mines and not airdropped floating mines, I'd say it's likely that they were German models laid by one of the raiders. The submarine Marlin and Dory discover is American (as evidenced by the "ESCAPE" sign), and the sub would have detailed maps of any Allied minefield.