Suggestion, it is doable, Cost, no idea other than not-cheap. If you are going to build up the dam so you can get concrete to your spot, and you want your dam to last as long as the house. Build a concrete dam into your existing dam that is designed for building your structure, make it one invoice and one total project together.
My rational is that if you cannot keep the house for "whatever reason" you are not going to be keeping the pond and dam either. So it might as well be a total mortgage bill for the entire development. If you have to sell, you got a real big ticket item to sell.

"Never Trust Government" -- Smart people.
"The Great thing we should Fear and the Weird Thing we Trust is Elon Musk" -- Me
"You can be broke but you cant be poor." -- Ruthie-May Webster