There is no actual reservoir at "reservoir #1" any more since its dam failed quite some time ago (anyone know when?). Now it's just a wetland which can be sort of seen just around the corner by the clearing up the hill from this cache. The bridge crosses its drainage stream. Some of the ruins are visible from the bridge.
Prior to the great downpour in 2015 this route used to be the main way to get from Broken Hill to Colonial Knob. Since the bridge by Spicer Park got wiped out the alternative route past reservoir #2 and over the ridge is now preferred (it may even be slightly shorter). But the track is still walkable if not as well maintained as it used to be. If you can't find a way across the stream to get here you may have to take the long way by going via reservoir #2, over the ridge, through junction D and past reservoir #1.
You are looking for a bison tube in a camouflaged hide.
Note that dogs are not permitted in this area. Quoting from the PCC web site:
Dogs are permitted off lead, but only in the exotic trees. Dogs are not permitted on the route up to the reservoirs which travels through native bush on the adjoining DOC scenic reserve (Colonial Knob).
Note that there is a new "Track Closed" sign before this cache. I could not find a justifiable reason for the sign so am leaving this cache in place for now.