An hour-long stroll through an oak forest, past clusters of blackberries, St John's wort, olive trees and butterflies, ends with the rewarding sight of soft, white sands and gently breaking waves.

On Karadere beach, in north-east Bulgaria, a smattering of families have set up camp for the summer, as they have done for years. But this year the happy-go-lucky mood has been punctured by fears that the small corner of paradise is under imminent threat by Bulgaria's first carbon-neutral resort.

Having been considered ripe for development since the collapse of communism 19 years ago, the area is set to be turned into a luxury €1bn (£780m) settlement. Dubbed the Black Sea Gardens, it will include five new hill towns, artificial lakes, a marina and an extensive leisure area and will be self-sustaining, thanks to biomass power and construction from local, natural resources, say the developers.

But the 540-acre (219-hectare) development, spearheaded by the British architect Sir Norman Foster, has enraged Bulgaria's growing band of ecologists.

They say it will destroy the Black Sea coast's last remaining virgin stretches of beach and will have a devastating effect on the rich biodiversity of an area which has environmental protection status under the EU's Natura 2000 programme, which aims to protect endangered species and habitats.

But the Bulgarian government's failure to enact regulations outlawing extensive developments in such areas has allowed coastal constructions to go ahead almost unhindered. Now there is hardly a stretch of the country's 220-mile coastline untouched by overdeveloped resorts. Locals are often restricted from accessing beaches whose entrances are flanked by security guards.

Construction of the Black Sea Gardens project, which Foster and Partner's website describes as "a series of car-free hill towns in an unspoilt setting of oak forests, meadows and river gorges", is due to start next year. Under the plans, 15,000 inhabitants of Sky Village, Wilderness Village, Meadow Village, Cape Village and Sea Village will be encouraged to leave their cars outside the settlements and go by foot, or use pools of electric cars and shuttle buses instead.

Sky is the first village due to be built, with the backing of a British-Bulgarian investment group. US, Russian and Saudi Arabian investors have expressed an interest in the other hill towns, according to the Bulgarian co-architects, Projects Ltd, which describes the resort as having something for every holidaymaker - "from sportish Club Med types to more contemplative, sleepy types".