I just got back from doing a recce along the HYD, Gulbarga, Bijapur route and the following is my observation:
1) The rivers are seasonal, except the Krishna River. Almatti Dam is a good spot to hit. The drive is good.
2) Being an arid region, with a rocky strata, there are a number of lakes big and small in the region. Some dry up, some don't. The ones that hold water through the year, are contracted.
3) Gulbarga lake itself can be fished. The fisheries office is on the road between the lake and the Gulbarga Fort.
Hope this info helps...