Large-scale fish kill has been reported in Ulsoor Lake yet again on Monday morning. This is the second time that such a fish kill has been reported from the lake. The earlier fish kill was reported in the first week of March this year. Though the fish kill was reported to civic authorities on Monday itself, the dead fish are yet to be completely removed from the lake. The site of fish kill in the lake probably also has answers as to what caused the fish kill. This part of the lake has seen heavy dumping of solid waste, including non-biodegradable plastic and wet waste, by those residing around the lake. Though Ulsoor Lake is said to be one of the better maintained lakes in the city, it also suffers from inlet of untreated sewage into the lake from surrounding areas, increasing the ammonia levels in the water. The sewage water is responsible for depleting the dissolved oxygen (DO) levels, causing repeated fish kills. B.E. Satish, chief engineer (Lakes), Bruhat Bangalore Mahanagara Palike (BBMP), said that while solid waste is not being dumped in the lake directly, its the waste dumped in storm water drains up stream that get washed into the lake due to rains. This only increases the toxicity of the water in the lake leading to fish kill. Unless the practice of dumping of solid waste into storm water drains is not stopped, it’s difficult to maintain the lakes, he added. A recent study conducted by T.V. Ramachandra and team from Centre for Ecological Sciences of the Indian Institute of Science concluded that the inlet of sewage and dumping of solid waste into the lakes was the chief causes for fish kill. The team had studied the March fish kill in Ulsoor Lake, apart from two other such fish kill reported in other lakes in the city. While a major portion of the dumped solid waste is bio-degradable, the nutrients seep into the water after they are broken down, which coupled with sewage, will lead to an increase in concentration of ammonia and other nutrients in the water, the report says. The report had also identified commercial rearing of exotic fish species, such as African cat fish, as another reason for the fish kill in the lakes. Rearing of such exotic fish is banned by the government, but continues unchecked, in many lakes in the city.
2016, The Hindu