I am not even close to being an expert but I do have a clay based ground water pond. After the 12" of top soil I have pretty clay soil with some sand veins (clay percent ranging from 19% to 38%). Then when I get to 8'-12' deep it turns to 100% clay. My water is what would be considered way too clear but is a pretty color. Anyways the pond is only 2 years old and it started to have plants growing in all of the soil types. Even at crazy depths I did not think stuff would grow at. I know I was worried about plants growing when I dug my pond. Even thought about planting some in there to get it started but life got too busy. I do have some woods about 30' from the pond which drop leaves in there which probably help with nutrients. I hope this helps.