Conservationists and authorities around Australia are mourning the loss of one of the environment’s fiercest defenders.

Australian Marine Conservation Society (AMCS) campaigner Felicity Wishart passed away in her sleep on Sunday night, leaving a profound legacy of advocacy and protection for Australia’s vulnerable aquatic ecosystems.

“Flic was one of Australia's leading conservationists and was a great and inspiring champion for the planet, the cause she dedicated her life to,” the AMCS said in a statement.

“For 30 years Flic played a fundamental role in many of the key environmental campaigns in Australia.

“Flic was a leader of seminal campaigns to protect the rainforests, to stop land clearing in Queensland, to confront the threat of climate change and national campaigns to protect the marine environment through the creation of a national network of marine protected areas and in her last, greatest and yet unfinished campaign, to protect the Great Barrier Reef.

“None worked harder, with as much grace and achieved as many results to protect our heritage.

“She was a beloved mentor and guide, friend and confidant, inspiration and leader, mother and partner.

“Her intelligence, warmth, wisdom and energy are irreplaceable.

“Her legacy will endure. Her fight is our fight.

“Our hearts are with her family, including her partner and two young sons at this tragic time.”

Ms Wishart emerged as an activist with a love of Queensland’s Daintree rainforest in the late nineteen-eighties, and became a senior leader of the Wilderness Society from 2004 through to 2013.

Wilderness Society national director Lyndon Schneiders has told ABC reporters that Ms Wishart was “a great and inspiring leader of the environment movement”.

“She dedicated her entire adult life, stretching over a period of 30 years, towards our shared cause and to the people of the environment movement in Australia,” he said.

“Flic's loss to the movement is immeasurable and today we grieve with friends and colleagues from across the breadth and length of our movement - the Earth has lost a true champion.”

WWF-Australia said it was honoured to have worked alongside Ms Wishart in her “last, greatest and yet unfinished campaign, to protect the Great Barrier Reef”.

“Our deepest sympathies are with Flic's family and friends and our colleagues at AMCS,” the WWF said in a statement.

“Flic helped to turn the plight of the reef into the number one environmental issue in Australia and a matter of concern for people around the world.

“At WWF we admired Flic for her warmth, humour, courage, intelligence, knowledge, passion, drive and tireless work ethic.”