Accumulated organic waste between the Malavoor vented dam and the road bridge of the airport road downstream of the dam across the Phalguni (Gurupura) reduced the dissolved oxygen level in the water thereby killing aqua fauna.
This was the finding of the College of Fisheries, Mangaluru, which went into the reasons for the recent fish kill in the River.
Gangadhara Gowda, professor and Head, Department of Aquatic Environment Management, in his report, stated that fish kill was due to very low dissolved oxygen (DO) concentration (0-0.2 ppm) prevailing in the mid and bottom water in the region, which is supported by high biological oxygen demand (BOD).
This, he said, caused the death of fin and shell fishes, mullets, crabs and shrimps living in the depths of the river.
He categorically stated that low DO level was due to increased load of organic matter from the discharge of waste water.
The area is also such that the accumulated organic waste is not flushed during high tide owing to the depth of the river.
Prof. Gowda however felt that the low faecal coliforms’ level downstream of the dam indicated that the contamination was of a non-human origin.
Water downstream the dam had faecal streptococci (animal waste) as high as 1.1 lakh MPN as against 230 MPN faecal (human) coliforms.
M.N. Venugopal, Dean, Fisheries, told The Hindu that the problem caused by organic waste multiplied because there was no exchange of water during high and low tides due to the sheer depth of river near the dam.
High tides might have brought waste from as far as Kudroli and Boloor, which got accumulated near the dam and never went back, he said.
Residents of the area allege that the river between the bridge and the dam has become a safe haven to throw loads of poultry waste and other animal waste.
There is no one to contain this practice, said Devarajan, a resident of Kottara and a regular visitor to the locality.
Mr. Devarajan also said poultry waste was also being thrown into Pachchanadi Stream, which joins the river upstream the dam.
KSPCB’s Scientific Officer Rajashekar Puranik said throwing of animal waste into the river has been rampant.
He has regularly been witnessing the practice since a fortnight during his regular visits.