Thiruvananthapuram: Silver dead bodies of fish cover Veli lake. The cause of this sudden fish death is unknown, though some experts at Fisheries Department believe that a drop in oxygen level caused by water hyacinth infestation as the reason. Some others believe that the reason could be the drop in water quality thanks to the untreated sewage effluents let out into the lake. The possibility of pollutants in the lake can also not be ruled out.
Experts will visit the site to ascertain the real cause behind this. “The water quality needs to be tested,” says A Biju Kumar, Head, Department of Aquatic Biology and Fisheries.
The phenomenon came to the attention of local residents on Monday. DC contacted officials at Fisheries Department, who have assured that they will visit the site on Thursday. They said that, a year ago, a similar phenomenon was observed. At that time, the reason was the decaying of water hyacinth, and the production of hydrogen sulphide, which causes fish mortality, they say.
But Veli lake being a confluence of sewage water, with Parvathy Puthanar river, Thettiyar canal and Amayizhanchan Thodu canal converging here, that in itself can cause a severe depletion of oxygen, according to environmentalist Sanjeev S J. “Recently a researcher studied the water quality of Thettiyar canal, and found that it had e-coli in abundance. The Biochemical Oxygen Demand (BOD) is quite low in polluted water,” he says.
Even treated sewage water can cause oxygen depletion, as some chemicals can cause algae bloom. There was rain, last week. If pesticides used in farms nearby polluted the water, the increase in phosphorus can again cause an increase in the growth of algae.
