The man who is believed to have hooked an otter while fishing illegally has contacted the authorities after a video of the incident went viral.

In a post on its Facebook page, wildlife rescue group Animal Concerns Research and Education Society said the man in question is assisting police with their investigations.

The incident, which occurred on a stretch of the Kallang River near Toa Payoh Lorong 8, was captured in a YouTube video posted on Tuesday by user Fast Snail, who has documented numerous sightings of the animals on his page.

The video shows the otter being hooked on a fishing line and crying in distress before escaping.

It had subsequently been seen limping with a fishing line and hook still attached to its right hind leg. However, in a video by Fast Snail posted on Thursday, it appeared to have broken free of the line and was no longer limping.

Fishing is not allowed in waterways and anyone caught doing so can be fined up to $3,000.

Otters have become an increasingly common sight in Singapore in recent years, having been spotted in waterways in Bishan-Ang Mo Kio Park, Punggol Waterfront and Sungei Buloh.

The threatened native species is found in marine and freshwater habitats, thriving in mangroves, river mouths and natural shorelines.

But illegal fishing is just one of the problems the otters face.

Mr N. Sivasothi, senior lecturer with the department of biological sciences at the National University of Singapore, said littering is another problem the emerging otter population is up against.

He has encountered otters caught in raffia and eating styrofoam. "People have to be more aware of the impact of their actions," he added.