At first, I thought a brahminy kite was flying low over the marsh but soon realised that this was not a kite but a harrier.... likely a juvenile eastern marsh harrier. The head of the harrier was very visibly pale and the rest of its plumage was in much darker tones of brown with a distinct white rump.
It made several passes over the marsh before flying off towards the north.
harrier @ kranji marshes 19Nov2016 from SgBeachBum on Vimeo.