Oh. I was right. Do I get a prize?
I took my war time aeriel recon photo from NCAP, David - the UK's museum for aerial recon images, all mainly from WW2. There were many of that part of the river opposite Vienna, and all showed up as in the image I posted above, which is actually pretty densely urbanised, more so than shows up on your maps, I think.
NCAP is a great site, though to view zoomable images you have to pay a small fee - £20 a year, I think.
Here's the other side of the alte donau loop. This was taken 13 April 1944. There's a park there - the donau park, I think, but it's not forest.
Image copyright - NCAP