One third of what Bengaluru now is actually the catchment area of Vrishabhavathi river, which flows southwest for about 50 km before joining Arkavathi river.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/5-million-litres-waste-water-chokes-vrishabhavathi-river-every-day
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/times-india-bangalore
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/karnataka
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/river-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/atree
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/industrial-pollution
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/heavy-metals
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-pollution