The pond the boys fall into was a man made pool because the crew wanted them to be "safe and secure" and didn't want to put them a real pond because they didn't know what was in it. But
Corey Feldman stated in a interview the joke of the whole thing was they built and filled it with water in June and by time they got to film the scene it was in August. So it been out in the woods for 3 month and they didn't know what was in it anyway.
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