Nine koi fish swim lazily around a clear pond, accompanied by two dark and placid sucker fish moving slowly along the bottom and edges.

It is a description which would not be out of place anywhere in Singapore, except that this particular "pond" is built on a multi-step entrance of a unit in a Housing Board flat.

The unit is on the ground floor of Block 415 in Tampines Street 41, a low-rise HDB block of flats.

The outside of the unit is decorated with lush greenery, and you hear the water before you spot the "pond" - a clear blue tank with its glass walls sealed to the concrete of the steps and wall.

Though the entrance is blocked, the residents in the unit can access their home through the adjacent unit, which is also owned by them.

When approached by The Sunday Times yesterday afternoon, the residents, a Chinese family, declined comment. But neighbours said the tank has been there for years.

"I have lived here for around six years, and the pond has been there for at least three," said Ms Nurfathiah Mohamad Fadillah.

The 31-year-old said she appreciates such a unique feature.

"It's something you cannot see anywhere else, and I wish that more people would do such a thing," said Ms Nurfathiah, who works in infant education and care.

Retailer Christina Ang, 59, said the family has lived there for at least 20 years, and the fish are pretty to look at.

"It is beautiful," said Madam Ang.

Engineer Neo Hock Lye, 43, said he does not notice the fish tank much as it does not block his way.

"But my nine-year-old and seven-year-old sons like to watch the fish swimming around," he added.

Mr Baey Yam Keng, an MP for Tampines GRC, visited the flat yesterday morning, and said the fish tank has become a part of the neighbourhood.

He said: "I was surprised to learn that it had been there for a few years already, and in that sense we can say that it has 'stood the test of time' - we have received no complaints from the neighbours."

Mr Baey said the tank looked properly constructed, and did not obstruct either the residents or members of the public.

"But after all, the outside of the flat is still a public space... I've asked the town council how we can legalise this tank," said Mr Baey.

He added that the family will work with the authorities to make sure issues like maintenance and wall painting would not be adversely affected by the tank.

"It would be a pity if they couldn't keep it, because this is creative," he said.