IMO, for a 2 acre lake build - you must save some topsoil!

If not, then you will have rains washing clay back into your pond for 1-2 years while you are struggling to get your groundcover plants growing. That is going to cost you depth that you paid good money to create.

As a builder, how much good topsoil do you put back over clay to establish nice lawns?

Also, gehajake actually knows how to do dirt work. Maybe he will pop back into your thread to say how much good topsoil should be graded back over the clay. I have no clue if you only need 6" or if you need substantially more.

I do know that 3' of compacted clay built on a flat grade is going to drain very poorly. Your grass or other groundcover is not going to thrive alternating between water-logged roots and scorching Texas summers.