Yes there are lakes that hold Mahseer, and the Forbes sagar lakes do have small ones now. There use to be monster mahseer in them (read Paul Boote) "Somewhere down the crazy river" "Shivasamundram".
Only one issue, can these really be classified as a lakes? because there is water flowing in and out at all times (flow is less or more depending on power generation requirements), but the periphery of the lake remains still and the water stands still. Not ideal waters for mahseer, but all the same they survive but congregate in the faster flowing areas, in wait of their natural food (smaller fish). The better the oxygen level, the more active they become, and the more they feed which results in growth (of course water tempreature and clarity has a lot to do with their growth).
Similar lakes exist in the north of India, and the mahseer survive in them, so also in dams in some states in the north where the flow is very slow in the summer months.
Take crocodile rocks near Galibori camp as an example, in summer it almost resembles a lake, but the water runs deep even in low water conditions, and some of the largest fish have been taken from it.
However mahseer flourish and grow to their biggest sizes in well oxygenated waters with rocky bottoms, which the lakes dont have.
So it seems that the mahseer has learnt to adapt to many varying water conditions and survived over the years inspite of the poaching and water pollution.
One thing is that if the water is too slow in a river and the heat very high, you will need to seek out the deepest pools to have any chance at a fish.
An advantage of fishing waters located after dams, is that there will always be water flow (released for power generation) even in the dry months, ensuring an opportunity for fair sport.
Hope i was able to answer some of your thoughts !