In January my in-laws moved to a new place. I helped him dig his pond out--I mostly watched and mike drove the scoop tractor. There were cat-tails that had penetrated the clay barrier. It held a wet mud and that was all. After we dug the muck and cat-tails it promptly rained. The pond only held a foot or so of water.
In February Tabitha decided that we need to raise some pigs for meat--another iron in the fire. After the pig commitment was made we promptly found out that we were pregnant. Mike agreed to take care of the pigs. He has a nice warm barn. The pigs were happy and grew to the bounds of their 20'by15' pen. He then surrounded his pond with 15 to 20 cattle panels and set the pigs loose.
they worked their magic. trodding the edges with their little feet, eating all the cat-tail roots and generally making a piggy mess. The pond got a chartreuse green bloom of algae and still looks really scary. Then it rained and rained. The pond held so much water that now he is concerned about overflow erosion. Rumor has it that now he can remove the pigs and the pond will hold water for many years.
the main downside is that it takes a year for the pond to become a healthy eco-system--or a swimming hole.