Lorna Parker, Great Fen project manager, said: “While it was amazing to see the transformation of this land from arable fields to wetland, we were very grateful to see the last digger roll off so that nature can truly take over.
“The rainfall has helped fill the new mere and channels, and wherever there is water, there is life.”
She said muddy edges around the waterways were ideal for insects and molluscs, which “will provide a feast” for wading birds like lapwings, redshank and snipe.
Parker said the site should be open to the public in the summer, enabling visitors to “experience the land returning to nature for the first time in more than 100 years”.