The accolade is an international quality mark for parks and green spaces and the Heath and Reach beauty spot is one of 2,208 UK winners.
The park has 400 acres of woodland, heathland and meadows for all ages to enjoy, and is known for its beautiful walking and cycling trails.
A spokesman for The Greensand Trust said: "After two years that have seen our parks and green spaces play a vital role for people through lockdowns as a place to relax, exercise and meet friends and family safely, the news that Rushmere Country Park has achieved the Green Flag Award is testament to the hard work and dedication of the small charity team which makes the green space a great space everyone can enjoy.
Huge fire destroys narrow boat on Grand Union Canal in Heath and Reach
No hosepipe ban in Leighton Buzzard says Anglian Water as area moves into drought
Changes to Schools for the Future programme will impact Shefford and Stotfold cluster and Aspley Guise
Cortney Batchelor jailed for four years over '˜one punch' fatal attack
Talented Linslade school pupil has work displayed in Royal Academy of Arts
"We are also involved in helping to manage a number of Bedfordshire Green Flag sites, but this award is one we are particularly proud of as we manage Rushmere Country Park, which we co-own with Central Bedfordshire Council."
The Greensand Trust chief executive Gill Welham added: “We’re delighted to see the hard work of our staff and volunteers recognised in this way for the third consecutive year.
“Feedback received from the Green Flag judges credits our team for a site which is clearly being well run, meeting all the public needs, while placing an emphasis on reducing carbon footprint and congratulates us on the standard and quality of this much-loved public open space.
"Our plans for future development using a holistic approach considering the prominence of the water bodies and wider historical features were also praised and we’re grateful for the recognition.”
Keep Britain Tidy’s accreditation manager Paul Todd said: “I would like to congratulate everyone involved in making Rushmere Country Park worthy of a Green Flag Award.
“Rushmere Country Park is a vital green space for the community in the Leighton Buzzard area. This award is testament to all the hard work of staff and volunteers, who do so much to ensure that it maintains the high standards demanded by the Green Flag Award.”
The Green Flag Award scheme is managed by the environmental charity Keep Britain Tidy under licence from the Department for Levelling Up, Housing and Communities.