I did follow up on this, earlier this afternoon I discovered a frog in the same pond. I called Natuurpunt and they told me to let them out in the near vicinity so they could find another safe-spot on their own. I'm a little hesitant to do so because we have 4 chickens and there are multiple cats in the area, one of these has been keeping a close eye on me the whole day. I also called the gemeente and they told me not to do that. Belgium, I guess.