Another idea is to contact a local landsaper or Exc contractor that sells a lot of top soil and give it to them. I am sure there is someone that would come in strip it and build your dam in trade for the top soil. Think I would hit them up for a nice aerator and nice diving area and waterfall on the spillway too.

1/4 acre [NOT BIG ENOUGH] about 10' deep [NOT DEEP ENOUGH] The weeds are taking over Saving up money to rent Exc, I sold mine. EX Pond Digger!