Help Grandmothers goldfish keep dying.

OK so my grandmother's fish until had a good number of goldfish in it but none of them survived the winter this year. She didn't get new gold fish early on because she knew the pond needed fixing up. So about the end of july the pond guy came out and fixed it up and a week later fish were put in. Now there are two left and I can't figure out why. It also seems like there is too much algee in the pond as well