I live 2 hours west of Dallas, and spent $7,500 to build a 5-7 acre lake...depending on if I can suppliment water to stabilize the drought periods, my land value will about double in value. $20,000 is pretty steep, but there aren't many places that can hold 10 acres of water. You will have to look pretty hard to find a tract of land to hold water that size...trust me, I'm looking, there's money to be made and lost developing a project that size and land investors see the opportunity.
