It is obvious that the surface waters of the Hussainsagar are polluted, but according to a study, the pollution extends to the depths of the historic lake, poisoning aquatic life and birds. The immersion of Ganesh idols only makes a bad situation worse.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/pollution-runs-deep-hussainsagar
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/deccan-chronicle-hyderabad
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/hussain-sagar
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/lake-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-council-medical-research-icmr
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-quality
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/total-dissolved-solids
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-pollution