Is the pond holding water 100%? If so, then bentonite is not the cure for what ails you.
I agree with jpsdad, that getting anything growing would be a good starting point. Converting bare clay into fertile "soil" is an organic process.
I believe there were some old threads where people had pretty good success getting rye started on their clay.
Are there any spots where you are sure you have a thick clay seal? If so, then you could disk or rake in some good topsoil and then lightly compact. Maybe you could get some patches of vegetation started in those spots.
