Designers and builders of the $6.4 million fountain, shaped like a water-filled sloping stone ring, watched as the fountain was filled. Visitors to the fountain in Hyde Park (search) will be able to splash in the water or picnic inside or around the oval.
"The princess was a contemporary woman. I wanted very much it to be a place you walked into. A total environment -- not an object you walked around," said Kathryn Gustafson, the American designer whose plan for the fountain beat 57 others.
"She was so inclusive that we wanted it to be something you felt you were part of."
The fountain will open formally at a July 6 ceremony where expected guests include the late princess' sons, William and Harry; her ex-husband Prince Charles (search); and members of her family including her brother, Earl Spencer.
It will be the Spencer family's first public appearance with the royal family since Diana's 1997 funeral, where Earl Spencer criticized the royals for their treatment of his sister.
Construction of the fountain, which consists of 545 blocks of Cornish granite, was delayed by bureaucratic wrangling and arguments within the Memorial Fountain Committee headed by Diana's friend, Rosa Monckton.
The Royal Parks and the Department for Culture, Media and Sport provided extra funds when the installation ran $1 million over budget.