The water level in the Yamuna river crossed the danger mark in the capital on Monday morning. The authorities expect the level to rise further, and have declared a "high alert".
The water level rose to 205.15 metres, 32 centimetres above the danger mark of 204.83 metres, as the Haryana government was forced to release nearly 50,000 cusecs of water from swollen reservoirs upstream on Sunday night.
The authorities in New Delhi have issued a high alert in neighbourhoods along the riverbank.
The water level is likely to rise further to 205.80 metres by Monday evening, an official at Delhi Government's Flood Control Room said.
On Sunday, the water-level in Yamuna had risen to 204.60 metres after the Haryana government released 400,000 cusecs of water.
The Yamuna has been carrying far more water than usual due to heavy rainfall in its catchment areas in the Himalayas. The reservoirs have also lost part of their capacity to hold water due to siltattion.