If you're on BC and you both were wearing clothing, it's possible but highly unlikely. Surely the pond water helped as well. I would not panic about it.
It is highly unlikely if you were just sitting on him and not doing anything else. Try to relax about this one. If you do miss your period, then that would be a time to be concerned. But without actually having sex, this doesn't seem likely ;)
...............VERY VERY VERY unlikely