This time, expert divers are poised to explore the murky depths of the dam, and digs will take place in woodland next to the water.
A lorry driver previously claimed he saw a woman handing over a child similar to Madeleine to a man at the reservoir, two days after she went missing from her Praia da Luz holiday apartment on May 3, 2007.
The reservoir was searched twice before in February and March 2008 by divers hired by a Portuguese lawyer.
Marcos Aragao Correia organised the privately-funded operation after claiming he had been tipped off by contacts that Madeleine had been murdered and her body thrown into the reservoir within 48 hours of her disappearance.