The district administration said the water level of all dams in Palakkad has risen following good rainfall in the past two days.
It was on Thursday evening that the man, who was on a visit to the Malampuzha gardens, jumped into the dam.
The International Federation of Red Cross and Red Crescent Societies (IFRC) also said that the number of victims could reach thousands.
The police are also looking at how the youth managed to take as many as 11 small locks inside the dam despite checks with metal detectors.
Idukki police have registered an FIR against the accused invoking sections of the Official Secrets Act, 1923 based on a complaint filed by KSEB.
With the dam being opened, water levels in Kakkad and Pampa rivers have risen.
India is on course to end the June-September monsoon season with a rainfall deficit of at least 8 per cent, say IMD officials
Though most of the areas of Walayar Dam come under Tamil Nadu territory, the total governing authority falls under Palakkad district administration.
No deaths were initially reported, but US spokesman John Kirby said the flooding had probably caused 'many deaths'
Over 40 elephants, including calves, are present near the human habitation, the Forest Department has confirmed.