The river rose to 5.85 metres (19.2 feet) early Monday, causing continued headaches for commuters as well as people living near its overflowing banks.
The Vigicrues flooding agency said the river would stay at its current level throughout the day before beginning to recede Tuesday.
"It's been a gradual rise, so you can't really call it a 'peak' -- we prefer to say it has plateaued," said Rachel Puechberty, a spokeswoman for the agency.
Light rain is forecast for Monday but it is not expected to push the Seine higher, though water levels are likely to stay high for at least a week, Puechberty said.
Around 1,500 people have been evacuated from their homes in the greater Paris region, according to police, while 1,900 households have lost electricity.