looks like from your photo you are going to dig a pit pond,so there won't be a dam. get a backhoe and dig a test hole about as deep as you can to see what the strata underneath looks like and to check for springs. then you can start to estimate if you can even make a pond work in that area. as far as fill goes for your foundation use a motor scraper to haul the fill in and spread it no deeper than 8 inches per layer then blade it off and with the full scraper drive over the fill track to track to compact. tear the surface up a little and start over and repeat until desired fill is in place. never fill on top of undisturbed vegetative top soil. remove it first with the scraper and stockpile it for use later. if you have ground water that comes up in the pit let it settle until it goes static and you can measure the overburden above the water and then estimate how much wet bank will need removed for your pond.