This is a nice little waterfall on the Bear Kill in Delaware County. It flows directly into the Schoharie Reservoir. Back in the day, this was probably a minor waterfall destination, as nearby Devasago Falls were considered a major tourist attraction. Unfortunately, Devasego Falls are now under the waters of the reservoir and obviously inaccessible. I missed a major once-in-a-lifetime opportunity, though. Apparently, back in 2006, the reservoir was drained to repair the dam, and Devasego falls were exposed for a time. I haven't found any pictures from that time, but someone must have taken some.
Anyway, back to the falls you can see. Dunn describes Hardenbergh Falls on page 92 of the Catskill Waterfall Guide. He spells it with an "e" in -bergh although it's spelled with a "u" on the Prattsville USGS topo map. Dunn mentions this and that it also may be spelled with just -burg so take your pick.
Speaking of pics, here's some from back in 2003. The entire reservoir is owned by the NYC Dept of Environmental Protection, and a permit is required to enter their lands and to gain access to the reservoir. A friend of mine had a permit (which I think is no harder to get than to just ask, and maybe pay a small fee) so we could go in to get pictures of the falls. Not that we saw anyone the whole time we were there, much less anyone asking to see our permit, but you never know. There were no fences or gates where we went, so there's nothing really keeping anyone from just walking down from the bridge where there's parking for a couple cars and look at the falls.
Here's a wide shot showing the falls, the bridge and the pool in the foreground, which is the surface of the reservoir.
A wide shot with the bridge cropped out. Not sure what the stone work on the left is from, maybe an older bridge.
A closer shot of just the falls.