Bill,
I spoke with Rick Wolffe about this. It turns out that Rees DIDN'T add a pond:
"On 18 Lower, Rees Jones did not add a pond. There has been a pond on 18 Lower since this golf hole was opened in 1922. One or two years ago, this existing pond, which runs laterally along the left side of the drive zone, was dredged and widened by about 5 yards in the rough towards the fairway. The rough grass between the fairway and the pond was removed and now the fairway runs alongside the pond. As originally designed by Tillinghast the fairway ran alongside this pond. The strip of rough which used to run between the pond and the fairway was put in place in advance of the 1980 US Open per the advise of the USGA. The existing dam, which is crumbling, will be replaced sometime in future before the 2016 PGA."
So here again is another example of his restoring the hole to the original design feature as Tilly had it...