More particularly, the "Big Ferghana Canal" modestly named after Stalin. Like so many other engineering projects of the era, this was built with Gulag laborer assistance.
The serial number for these is on the screwback. I've got a couple of them with original screwbacks (s/n's in the 40k and 70k-80k range), and one that someone converted to a pin-back. It's a nice badge. They are a little tough to find now.
I don't seem that often anymore, even in Tashkent. I got mine from Kokand in the Ferghana Valley. Now I guess I need to see the canal itself just to go full-circle.
Marc - straying a bit into other-thread territory, do you have any clues on what to look for in the fakes? I've been able to get mine very close to the "source", but I'm sure I'll see others out there.
...Brian
There's also a Tajik version of this badge that looks identical except for the republic notation at the bottom of the badge. They are really hard to find. I've only seen one or two, and wasn't willing to pay the price.