Wildlife conservation champion Lady Philippa Scott, of Gloucestershire, has died, the Wildfowl and Wetlands Trust (WWT) has announced.
Lady Scott, 91, was honorary director of the WWT founded by her late husband, wildlife TV presenter, Sir Peter Scott.
It is understood she suffered a fall at her home on the trust's Slimbridge site late last year and moved to a care home after a spell in hospital.
Lady Scott died on Tuesday night, the WWT said.
Martin Spray, chief executive of the WWT, said: "There is a saying 'behind every man is a great woman' and this was never more true than of Lady Scott.
"Sir David Attenborough famously said that 'the Scott partnership put conservation on the map, at a time when conservation was not a word that most people understood'."
Lady Scott married Sir Peter in Reykjavik, Iceland, in 1951 after an expedition to ring pink-footed geese.
Her husband died in 1989, aged 79.
Mr Spray said: "Lady Scott remained committed to and passionate about the work of WWT, holding the post of honorary director up until the end of her life.
"She will be sorely missed by staff, volunteers and members of WWT."
Lady Scott was a scuba diver and fish watcher, and was an honorary life member of the British Sub Aqua Club (BSAC) and president of its Cotswold branch.
She was also patron of the Gloucestershire Wildlife Trust and president of the Nature in Art Trust.
The WWT said her special interests included Antarctica, which she visited six times, and the great whales.