A new Marine Indigenous Protected Area has been given the green light, making it the largest marine area under Aboriginal management in the Northern Territory.

The declaration on Thursday means 2.7 million hectares will now be under Traditional Owner management, adding 861,300 hectares of Sea Country to the existing Southeast Arnhem Land Indigenous Protected Area.

While the existing Southeast Arnhem Land Indigenous Protected Area (IPA) has been under Aboriginal management for over 10 years, this extension signifies the importance of protecting the biodiversity and conservation of precious Sea Country.

Located in the western Gulf of Carpentaria, the IPA provides critical refuge for marine wildlife threatened elsewhere by coastal development, pollution, and maritime traffic.

This sea country IPA will enable ranger teams to monitor vulnerable or customary marine species such as dugong and turtles, and better manage major threats such as ghost nets, marine debris and illegal fishing.

Clive Nunggurgalu, Senior Numburindi Numbulwar Ranger and Traditional Owner, said: "We are the caretakers and custodians of this Sea Country.

"It is our responsibility to care for it and make sure it stays healthy for all future generations," he said.

"Today is an important recognition of the work we have already being and will continue to do to care for our Country - both the land and the sea."

The new area also includes a shared 43,948 hectares over Blue Mud Bay with Laynapuy IPA, ensuring continuous Indigenous ranger presence across the western part of the Gulf of Carpentaria.

Beyond Caring for Country and the protection of cultural heritage, the IPA and its embedded ranger groups have consistently advanced training, education, meaningful employment, and self-determined governance in the Aboriginal communities of Ngukurr, Numbulwar and surrounding homelands.

Northern Land Council chairperson, Matthew Ryan, noted that "for over 60,000 years, Aboriginal people have managed and taken care of our land and sea".

"This declaration is an important recognition of that work and the importance of listening to Traditional Owners who are the experts of taking care of and protecting land and Sea Country," he said.

"It is wonderful to be here alongside Traditional Owners to celebrate this important declaration of Sea Country as part of the Southeast Arnhem IPA, and I thank them for all their hard work getting to this point."

IPAs are supported by the federal government and provide a platform for local communities to establish partnerships with research, philanthropic and industry bodies to advance community aspirations and autonomy. The new declaration will mean extending these environmental, cultural and economic benefits out into marine areas as well.

Stage 1 of the SE Arnhem Land Indigenous Protected Area (IPA) was dedicated in 2015. The Sea Country expansion (Stage 2) spanning 861,533ha has been in development for years, with many Traditional Owners and stakeholders involved.

Covering marine areas associated with the ancestral estates of South East Arnhem Land's Traditional Owners, the Sea Country IPA holds powerful songlines and dreamings. With stunning river systems, billabongs, estuaries, reefs, islands, freshwater floodplains and cays, the Sea Country IPA extends from the high-tide mark seawards to 140 kilometres off the coast, taking in around 300km of coastline in total.

South East Arnhem Land Sea Country IPA covers both subtidal and intertidal zones and has many significant values including extensive seagrass meadows and nationally important mangrove-tidal wetland habitats and 8 pristine estuaries. It's also a vital habitat to dugongs, dolphins, nesting flatback, green and olive ridley turtles, seabirds and hosts four out of five of the world's sawfish species.

The mudflats between Wuyagiba and the lower Roper River are among the most important areas for migratory shorebirds in the NT with the IPA's freshwater floodplains supporting large numbers of waterbirds from the brolga to jabiru, ducks, magpie geese, and black swans.

Majority Indigenous-led environmental not-for-profit group, Country Needs People, welcomed the announcement and congratulated Traditional Owners.

"Huge congratulations to all the Traditional Owners in South East Arnhem Land who've worked so hard over so many years with key support from the Northern Land Council, to make their dream a reality, to include Sea Country in their existing Indigenous Protected Area," said the group's CEO, Patrick O'Leary.

"With environmentally and culturally significant Sea Country now recognised as part of your IPA, this adds another layer of protection for precious river systems, billabongs, beaches, coastline and islands into the future."