90 per cent of city's lakes dying

Energy CES Envis IISc

SEETHALAKSHMI S

Nearly 90 per cent of Bangalore's lakes are on the verge of extinction and the dissolved oxygen content of the water in the city's lakes has gone below the desired level of 4mg/lt due to organic pollution, a study conducted by the Karnataka State Pollution Control Board (KSPCB) has revealed.

The study which covered 60 lakes in the city has found out that most of the lakes are infested with weeds and the area near the lakes has heaps of garbage, faecal matter thereby making the water bodies completely unfit for recreation.

The advent of long-distance pumping and filtered water supply in the city had converted lakes into sewage-discharging ponds and garbage-dumping sites. ``Lakes are getting degraded beyond the point of recovery. Encroachment, siltation, weed infestation, discharge of effluent both industrial and domestic are knelling the death for lakes in Bangalore,'' KSPCB Chairman Upendra Tripathy said.

Take the case of Dasarahalli lake, where the dissolved oxygen (DO) level is less than 0.3 mg/lt due to industrial effluents from the Peenya industrial area and from nearby residences. The situation is worse at Lalbagh lake, where besides being polluted due to sewage leakages, major portion of the lake is occupied by weeds and the DO level is a mere 1mg/lt.

To top it, some of the lakes have been converted to residential localities, while some have been used by state departments for public purposes like bus stand and stadium, the study has revealed. And for lakes situated on the outskirts of the city, it is discharge of toxic substances, including untreated urban sewage and industrial effluents, pesticide and fertiliser run off from agricultural fields, Tripathy said. With this, some of the lakes in Bangalore are in the advanced stage of eutrophication __ an increase in the organic and inorganic nutrient content of the water body, resulting in an unbalanced ecosystem.

The study conducted over two years has found that most of the water bodies are polluted on account of discharge of sewage effluent. ``Layouts coming up on the outskirts are also releasing untreated sewage effluents which get into nearby water bodies instead of reaching the sewage treatment plants,'' Tripathy said.

According to environmentalists, municipal effluents get into these lakes, due to the absence of proper sewerage system in the city. ``The adverse effect is there for all to see __ depletion of dissolved oxygen affecting aquatic life, mosquito breeding causing health hazards, growth of water hyacinth and other aquatic plants which cut off sunlight affecting photo-synthetic action,'' an activist lamented.

Sadly, though there are established sewage treatment plants for the three catchments of the Bangalore Metropolitan areas, these plants are under-loaded and bypasses are taking place into lakes, officials admit.

The Vengaiah lake in South Bangalore is the best example for unplanned sewerage treatment. The lake is polluted due to untreated sewage discharge from Ramamurthynagar and from the nearby unplanned urban settlements. Result: It is covered with weeds (water hyacinth) and the DO level is below 1.6 mg/lt.