Working on the pond. Any suggestions on how to keep water in it? Asking for a friend. 💦 
Discussion
If you’re going fully natural, a clay soil that is heavily compacted will do a fine job but a PVC liner will be a good option if you haven’t got any clay in the soil . If you’re looking to spend some more money an EPDM rubber mat will be the most durable. Make sure there’s no sharp edges objects that can break through the layer.
My brother runs an excavation business and looked at the soil. Looks like clay. Not sure what water source you’ll use.
If clay-dig the hole, pack it down with the bucket, fill with water.
If sand is deeper or a mix of sand and clay-dig the whole, dump in 6-8 pounds of bentonite per square foot, fill with water.
Thanks! It is clay down after the topsoil. The sand I put in as part of a failed experiment. The water table is almost up to the surface in the wetter parts of the year. I am also planning on running overflow from the house and the rest of the property into it as well.
Bentonite clay. Or just get a big ass rubber tarp and staple it down on the edges. I laid down a “mud retention grid” on top of that then packed dirt on top of that so the tarp isn’t even visible
PIGS! Mine would go dry in one day after filling up from a big rain. Installed a hot wire mesh fence around it and inserted two piglets. When they were ready to butcher, the pond was sealed! That was 3 years ago, still holding water.
As mentioned, bentonite clay, hogs, or a sheepsfoot roller.
It seems your hole has been dug for a while, long enough for grass to grow, but I can't really see evidence that it's retained water yet.
I see a very well-defined horizon break where the soil layers change.
When you get a chance, post a closer picture of the soil profile and tag me. Can't really determine clay content from an image, but I might be able to notice something that may help.
Thanks. It has been dug for a couple of years. The water table during the rainy parts of the year is almost to ground level. I will get you a better picture but the light brown on the walls is clay. From there down it is all clay.
Bentonite