And this video shows a fight between two rival groups:
A Redditor explains:
The larger group on the right is the Bishan family, the largest family of otters in Singapore. They are highly aggressive and expansionist towards other otters, and are the most famous and well documented family in Singapore. They have, to our knowledge, won every single fight against other otter families, no doubt due to their sheer numbers which makes them three times the size of a wild otter family.Wikipedia:
The group on the left is the Marina family, the second largest family in Singapore. They are known for constantly feuding (and losing) with the Bishan family, and being highly adaptable to urban areas, having learnt how to climb ladders and navigate storm drains.
The Bishan Otter Family, also known as the Bishan 10 and previously known as the Bishan 5, are a family of smooth-coated otters that reside in Singapore.
The otter family starred in the David Attenborough documentary Wild City and their exploits are frequently covered by the Singapore media. In 2016, the otter family was voted by The Straits Times readers to represent Singapore on her 51st birthday, beating Singlish, the thumbdrive (which was invented by a Singapore company), the Singapore passport
On 11 June 2017, members of the public intervened to protect the Marina otters from their Bishan rivals by scaring the latter off with loud noises. The incident sparked an internet debate concerning human intervention in fights between the two otter families.