They look like the ones behind my pond, and about the same distance. My pond leaks and the excess water killed most of the trees below the dam except the cedars. They don't look too close to me. If you have a bunch of seepage they will likely die the first year after filling.
If they are below the toe of the backside, they probably won't hurt the dam unless they are willows or soft maple, which can send roots a hundred feet to water in some cases.