The State Pollution Control Board in a letter has asked the Irrigation Department to maintain average lean flow in the Periyar to avoid discolouration of the waters and recurring fish kills.
The letter, dated April 11, was sent by the board on the inference that the , especially during this summer. A case of fish kill was reported last week.
Tests held on March 30 had revealed that the dissolved oxygen level was almost nil in the downstream stretch of the river. The situation emerged after the closing of regulators at Manjummal and Pathalam, which had obstructed the environmental flow in the river, according to findings by the Environment Surveillance Centre of the board at Eloor.
The State Level Monitoring Committee constituted by the National Green Tribunal had asked the board in April last to ensure that the Irrigation Department adhered to directives of the tribunal for maintaining average 15 to 20% lean season flow in the river to avoid depletion of oxygen levels.
The closing of regulators in summer results in stagnation of river water. It leads to the accumulation of waste materials upstream at the regulators. The analysis of water samples collected on March 30 and April 7 found that the dissolved oxygen levels at the upstream and downstream of both Pathalam and Manjummal regulators were very low.
The board recommended that the Irrigation Department minimise the operation of the Purappallikkavu regulator and regularly operate the Pathalam and Manjummal regulators to avoid stagnation of river water. Wild growths on the riverbanks should be cleared to find out whether there is any discharging of effluents from industrial units. The department has to find out whether there are any unauthorised pipelines in the river.
The department should take action as per the Periyar Rejuvenation Plan and according to the directives issued by the NGT, the board said.