Cotswold Water Park has been given special status to protect its bird and plant population.
The 40 square mile site with its 177 lakes has been designated a Site of Special Scientific Interest by Natural England.
The park, which straddles Gloucestershire, Wiltshire and Oxfordshire, has been recognised for its biodiversity and its importance to breeding and watering birds.
The government organisation says the completely man-made site is a leading example of how people and nature can thrive side by side.
Marian Spain, Chief Executive of Natural England, said: “I‘m delighted to announce that Natural England has granted SSSI status to the Cotswold Water Park.
"Places like this are ever more important in bringing people and nature together, and giving us that contact with wildlife that’s so vital for our health and well-being.
"This extended designation is a testament to the efforts of the many bodies and individuals who have been involved in creating and managing the Water Park over many years, and living proof that some of our most important species can thrive hand-in-hand with homes, business and recreational activities.
"Special places like this form the vital backbone of a nature recovery network.”
The lakes were created when pits left by the extraction of limestone gravel along the upper River Thames filled naturally with water in the 1970s.
In 1994, 10 lakes were granted SSSI status for their aquatic plantlife. The park has since become of national importance for its bird and plant populations.
The new designation includes all 177 lakes, protecting the large populations of breeding and wintering birds that live there, as well as the aquatic plants.
The park is a popular leisure spot, offering water sports and beautiful walks, but also often benefits wildlife. For example, the sailing clubs manage some areas as scrub, providing the perfect habitat for breeding birds.
Cotswold Water Park provides a home for scarce species of birds, including little egret, little ringed plover and nightingale, with around 35,000 waterbirds present over winter.
The scrub and reedbed are also full of a variety of warblers.
Paul Hazel, Chairman of Cotswold Water Park Trust, said, "The Trust is pleased that Natural England has now formally recognised the significance of the Cotswold Water Park’s biodiversity, and in particular its importance to breeding and wintering birds...
"It is crucial that the Cotswold Water Park moves forward as a balanced and sustainable example of how wildlife and people can successfully coexist, and that the public can continue to enjoy the benefits of living in, working in, or visiting this unique area."