[UPDATE March 31] Otters managed to find a way to the koi pond despite a recent height increase in the glass barricade, the Gardens by the Bay told AsiaOne.
They did not disclose the number of koi that were affected by the incident.
The otters got in through the fence at the back of the pond, said the Gardens by the Bay, adding: "We will be reinforcing the fence while rehousing the koi to another location".
For this hungry monitor lizard, it happened to be at the wrong place at the wrong time.
The reptile "decimated" the koi pond at Gardens by the Bay, Redditor Babyboo8 said on Wednesday (March 30).
According to the Redditor, many of the fish were "torn in half", with "only a small handful still alive and hiding in corners of the pond."
But after Babyboo8 spoke to a park ranger at Gardens by the Bay, he found out what was behind the kois' deaths.
"It was an otter attack. The monitor lizard only feeds on dead fish so it was just 'cleaning' up the otter's mess," he wrote.
In the comments, some Redditors cheekily pointed out that the monitor lizard might feel offended by the accusation.
One of them just had enough of the otters' antics and their huge appetite for ornamental fish.
Otters here have a history of seeking food outside of their natural habitat.
On March 13, several otters sneaked into an elderly man's house and left headless remains of his koi and luohan fish behind.
Last year, over 100 fish were gobbled up by otters in four days at the Church of St Teresa. Some of the koi had been raised by church staff and gardeners for more than 15 years.