The government has issued a 14-day notice to owners of Seefar Apartments in Nairobi's Nyayo Highrise estate to bring the building down.
In a notice on Friday, the National Environment Management Authority (Nema) and Water Resource Authority (WRA) ordered the property's developer, Edermann Property to demolish the structure over claims that it sits on Nairobi Dam's riparian reserve.
The two agencies said the residential building is interfering with the flow of Ngong River and ordered the developer to also restore the reserve within 90 days.
"Demolish the structure within 14 days effective this order, failure to which it will be pulled down without further reference to you," the order reads in part as quoted by The Star.
Nema further noted that the 12-storey building, which has 260 houses, was constructed in contravention of Cap 387 of the Environmental Management and Co-ordination Act (EMCA).
Seefar Apartments proprietor John Rajwayi has however denied claims by the environment authorities that the expensive structure was illegally built.
"They told us that they misplaced the instructions in the file and we expect them to come on Monday to cancel the order since we followed the laid down requirement."
Rajwayi added: "The building is 22 metres from the dam and is, hence, way far from the boundary line."
The crackdown on illegal structures in Nairobi, which targets more than 2,000 buildings, has seen some expensive buildings including the South End Mall, Ukay Mall, Taj Mall among others flattened in the last few weeks.