On my new 1/4 acre pond that is just filling, there is a white ring about three feet up the bank from the water, and maybe 8 to 10 vertical inches above the water. The ring is at the upper line of the wet clay that is absorbing water that is wicking up the banks on the dam. The ring is about six to ten inches wide. What could this be? The pond is in all red and gray clays.

Here's a picture.

Minerals???

Just a wag on my part.

Cmm

+1 Looks like something is coming out of solution as the water evaporates off. Interesting your other ponds don't show the same thing. Did you do anything different to this pond than the others, like add Alum, lime or some other treatment?

John F,
If you were in SE Texas where I am, I'd just say it was white clay settling out....

My other pond did that a little bit, but quickly became grassed over since it was renovated in August 2015, so I didn't notice it if it happened. It looks like a salt ring, but there is virtually no salt in our runoff waters. Must be something leaching out of the clay?

I agree....keep an eye on it. If you see no ill effects to your pond, I wouldn't fret over it too much. When my pond was renovated in 2014, I had a reddish brown line of oily seepage coming out of a seam about 8' down in one corner of the pond...not much, just enough to notice. When the pond was compacted and filled, I have never seen any residue on the surface what so ever. An old neighbor that's lived there all his life (and has several ponds) indicated that he's seen the same phenomenon over the years and never knew what it was....just something leaching out a seam in the strata of the soil.

Salts.

We see this occasionally in fields that have spots that are perennially wet. The high water table floats the salts to the surface.