Hello and welcome! My iPad isn't loading your entire message, or the pic --- no, there it went!
That is a nice pond, or planter, but I wouldn't trust that concrete! If it was me, I would consider installing an EPDM liner. What is the pipe sticking up from the middle? Was that for a fountain?
And where to you live? If it's already frozen and cracked [as you suspect], then I would be afraid it would happen again, which you wouldn't want to happen if it was housing fish.