What's this white liquid flowing out of drain at Bishan Park?

Stomper LEK sent Stomp a photo showing an unknown white liquid flowing out of a drain at Bishan Park 1.

In a telephone interview, the Stomper said that he came across the unusual sight yesterday (Jun 24) at around 5.53pm.

Based on the photo, the liquid had turned parts of the stream at Bishan Park white.

The Stomper said that this has been going on for years. 

He told Stomp that this happens on an average of one or twice a month.

LEK also reported seeing foam and dark-coloured liquid flowing out the drain on several occasions.