A multi-million-dollar bequest from an American benefactor has shocked a volunteer wombat rescue program in South Australia.

The man visited Mannum in South Australia to see the work two years ago and has now given $8 million to the Wombat Awareness Organisation.

Founding director Brigitte Stevens has been astounded by the donation and plans to put the money towards buying land to develop a centre to care for wombats.

"There's nothing like that in South Australia and you know that'd be a big step forward for conservation in South Australia where we can then work on co-existence with other species of wildlife as well," she said.

"My heart is always with wombats, they're the love of my life and there's so much work that needs to be done.

"But it's about finding other people that have got that passion for other species of wildlife that can work with us and also offering the wildlife carer community a better service."