Increasing algal bloom in the Tungabhadra river has led to it turning green. Experts believe that a rapid growth algae or cyanobacteria in water has resulted in a coloured scum that collects on the surface. Wildlife activists and researcher owe this to pollution of the river. It is believed that farmers in the upstream use chemical fertilisers for agriculture which gets washed off during the monsoon and gets collected in the river. Industries too release untreated effluents, resulting in eutrophication or algal bloom. 

Cyanobacteria is said to bloom rapidly in cloudy weather followed by sunshine. Though it is short-lived, they absorb all the oxygen and nutrients in the water and grow rapidly. Even when they start decaying, they continue to use the oxygen in the water. Speaking to the Bangalore Mirror, wildlife activist and researcher Samad Kottur said, "We have observed that long-term consumption of the water leads to liver disease and if people swim in the affected water, they are likely to develop skin rashes. It is advisable to avoid drinking this water for the next 10-15 days, and cattle should also be kept away. We have been observing this phenomenon for long, but in the last four-five years it has been happening often. While it was generally reported in November-December, this year it was spotted early. Awareness on this is being generated.”

Meanwhile,  D Ranga Reddy, the secretary of Tungabhadra Board said that the water will continue to be safe for drinking since the water outlet for consumption is different and the level is way below the level of the sight of the algae. He said this happens because of the pollution on the shore. The algae are formed in one feet of water when they are subjected to heat.  For instance, the water level was an approximate 80 feet on Thursday, and the greenish colour was recorded on the top one-and-a-half feet.