Logistics manager Alvin Tan lugs a 15kg camera bag containing two long camera lenses to work almost every day.

He wants to be prepared should a message about an otter sighting pop up on Finding Toby, the otter-watch WhatsApp group that he belongs to.

He rushes to join the group, made up of about 20 otter watchers, as soon as he finishes work or before he goes to the office. The 44-year-old enjoys taking photos of the mammals, especially their pups because "they have this blur look which I find very cute".

His weekends are often spent "chasing" otters all over Singapore. His accounts administrator wife, 44, and 11-year-old daughter sometimes join him on these trips.

He has taken more than 10,000 photos and 100 videos of the otters in the last six months and shares them on social media. "The otters have become like family. I want to know how they are doing. They seem to recognise faces and will not run away when they see a familiar face."

Mr Tan is part of a growing community of otter watchers, or "chasers", here. At least five groups devoted to this activity have sprung up in recent years. They are made up of students, working adults, researchers and retirees who notify one another of otter sightings via their respective WhatsApp chat groups and share photos and videos of the otters on social media.

Finding Toby, named after a pup the community rescued, was founded this year by Mr Jeffrey Teo, 45, a senior director in the financial services industry who started photographing otters four years ago.

The group provides updates almost every day on the whereabouts of the animals via WhatsApp.

OtterWatch, headed by National University of Singapore (NUS) biology lecturer N. Sivasothi, was set up in 2011 for researchers and otter enthusiasts. It has about 10 members.

Other groups include Otter Chasing, for those who are into photography and videography; Utterly Otterly for academics and students; and the OWG or Otter Working Group. OWG is a more formal one which brings together the public and various government and other agencies involved in the welfare of otters.

The regular updates by otter watchers have benefited at least one group here - those who are doing research on the mammals. NUS environmental studies undergraduate Max Khoo, 23, who did a project on otters last year, says: "On some occasions, it has helped me locate the otters more easily."

Mr Teo says one possible reason for the growing interest in otters among the public could be the increase here in what is known as the smooth-coated otter. Named after its velvety coat, it is the largest otter in South-east Asia.

According to Mr Sivasothi, the smooth-coated otter, listed as critically endangered in Singapore, was first sighted at Sungei Buloh Wetland Reserve in 1998, after an absence of 30 years.

The population has since grown and it is estimated that there are now six to seven families, consisting of about 50 otters in total, living along the shores and waterways of Singapore in areas such as Lorong Halus, East Coast Park, Marina Bay, Pasir Ris Park, Keppel and Ulu Pandan.

Probably the most famous families are Marina 9, first sighted at Gardens by the Bay in 2013, and Bishan 10, first sighted at BishanAng Mo Kio Park in 2014.

Bishan 10 have starred in a documentary about wildlife in Singapore, narrated by famed British naturalist David Attenborough, and were also recently featured on BBC News with the headline, "Singapore's celebrity urban otter family".

Mr Teo says the park connectors have brought people closer to the waterways, so it is easier for them to spot otters. He adds: "There is also a growing community of nature photographers and otters are an interesting subject for them to photograph."

He says the best time to spot otters is in the early morning between 6 and 10am and in the afternoon between 4 and 7pm.

The mammals like to play as a family in the water. After catching and eating fish, they often come on land to defecate. Then, they take a nap in their holt or nest before swimming elsewhere.

Mr Teo believes that urbanites are drawn to the otters because of their carefree lifestyle. He says: "They eat, play, swim, sleep and go sightseeing from Bishan to Upper Peirce, for instance, as a family. They are doing what we would like to do as human beings, but don't have time to because of our busy lifestyle."

The otter watchers are protective of the creatures and have jumped to their rescue more than once.

In April this year, when Ms Yane Kang, 40, a member of OtterWatch, saw that a pup had a fish hook near its eye, she posted a photo online. The group continued to check on the animal daily until it was sure that the hook had come off and the animal was doing well.

A month later, another member from the group discovered that a pup had been abandoned by its family. The group took turns to monitor the animal throughout the day. That afternoon, the pup almost drowned when it fell off a ledge into a canal.

Otter watcher and retiree Patrick Ng, 60, jumped into the canal to save it and left it in its holt in case the family came back. With no sign of the family returning, the group sent it to Wildlife Reserves Singapore for treatment in the evening.

Over the next few days, the otter watchers continued to comb the area nearby and eventually found the pup's family. With help from Wildlife Reserves Singapore, NUS and National Parks Board, the pup was returned to the pack.

Mr Tan, who was involved in the search and witnessed the reunion, recalls: "It was an emotional moment. We felt like foster parents returning a child to its real parents."