Fighting Fire with Fire

As reported by The Times of India, the Municipal Corporation of Hyderabad recently released 200,000 gambusia fish (Gambusia sp.) into India's Hussain Sagar Lake, in an attempt to control mosquito populations. Problem is that gambusia themselves are a known invasive species. But there continues to contraversy in India about the introduction: while some claim that the fish dine solely on mosquito larvae, others insist that the fish are a threat to the native flora and fauna of the lake. I'm a bit confused myself, since it appears Hussain Sagar Lake is a man-made body of water (though it is over 400 centuries old).