Singapore has two species of otters: the Smooth-coated Otter (Lutrogale perspicillata) and the Asian Small-clawed Otter (Aonyx cinereus). 
In Singapore, the Smooth-coated Otter is much more common than the Asian Small-clawed Otter.
The Smooth-coated Otter is quite large (up to 1.3 m, including tail) while the Asian Small-clawed Otter (up to 90 cm, including tail) is the smallest of all 13 species of otters found around the world.
The Smooth-coated Otter has a rounded head and and its tail is flattened, in contrast to the more rounded tails of other otters (clearly visible on the photos).

I found this individual in the canal next to Pasir Ris Park where it was swimming.
At one moment, it came out and and placed a good turd on the river bank.

Pasir Ris Park, Singapore, 24 October 2022