Mangaluru:The recent dead fish sightings reported near Raikatte Bridge in the backwaters of the Gurupura (Phalguni) River were likely caused by untreated sewage inflow, water stagnation, and depletion of dissolved oxygen, according to an inspection by Karnataka State Pollution Control Board (KSPCB), Mangaluru.KSPCB regional officer, Mangaluru, said the office received a telephonic complaint on Feb 9 about fish deaths and blackening of a stormwater drain near Raikatte Bridge, which joins the Gurupura backwaters.During an inspection the same day, officials found sewage flowing through the stormwater drain into the backwaters. The water appeared blackish, and several dead fish were found in the drain connected to the river. Preliminary observations indicated that the deaths were due to depletion of dissolved oxygen.Water samples from different locations were collected and sent to the KSPCB regional laboratory in Mangaluru for analysis. The department of fisheries also collected fish samples, and the results are awaited. Officials said no industrial effluent discharge was observed from industries in the Baikampady industrial cluster during the inspection.In a follow-up inspection on Feb 10, officials noted ongoing construction of the Kulur Bridge and the bridge connecting Sultan Battery and Tannirbhavi Beach. The Sultan Battery–Tannirbhavi Bridge project, spanning about 350 metres, involved filling portions of the river with soil.Officials said this disrupted natural tidal flushing up to the Maravoor vented dam. Combined with untreated sewage and limited freshwater flow, this led to stagnant conditions. High summer temperatures intensified biogeochemical reactions, causing a sharp drop in dissolved oxygen levels and resulting in fish deaths.The report noted that residential areas around Raikatte, Kulur, Baggundi Lake, Kodikere, Kudumburu Colony and Angaragundi, along with godowns and commercial establishments in the Baikampady industrial area, contributed to sullage. The area lacks underground drainage and sewage treatment plants. Related cases are already before the National Green Tribunal.Following the inspection, KSPCB directed Mangaluru Smart City Ltd to install culvert pipes to ensure flushing of the backwaters, and asked Mangaluru City Corporation to stop sewage inflow through stormwater drains and submit an action-taken report. Karnataka State Coastal Zone Management Authority was asked to clarify whether the bridge project complied with Coastal Regulation Zone norms.Officials said culvert pipes have since been installed, and the condition of the backwaters and the affected river arm has improved.
