Which Nallah? What Drain? JC Nagar to Ulsoor Lake.
Unlike the drain that comes in from Shivajinagar which bypasses the Ulsoor Lake, this drain empties itself into the lake. Ideally, it's only rainwater that should flow through, but in reality there are enough slums and houses on the way emptying sewage and contaminating the water and colouring the lake green.
However, the Assaye Road stretch of the drain is not flanked by homes or scrapyards and just before Ulsoor Lake, the Bengali Association has been allotted a drain side home. These pictures are from the hall by the drain where Ganesha and Durga idols are being made year round in preparation for the festival season.
And like Agujral points out in comments: The idols will end up in Ulsoor lake (not in the dirty drain)