Lebanese protesters raise a national flag as they take part in a 20km march in the Bisri Valley. Joseph Eid/AFP

Surrounded by sweeping pines, lemon trees and bean stalks, hundreds of Lebanese protesters march along, chanting against a planned dam that would drown the valley under their feet.

Unprecedented protests about corruption in Lebanon since October 17 have given new life to activism against the controversial structure planned for a lush valley south of Beirut.

Since the start of the year, the future construction site in the Bisri Valley has been cordoned off and several trees uprooted to make way for work to begin.

A Lebanese protester rests with national flag as she takes part in the march in the Bisri Valley. Joseph Eid/AFP

But emboldened by the anti-graft protests, nature lovers have since November 9 ignored the gates and barged through them, hoping to save what remains of their country's ravaged ecosystem.

Environmental activists in Lebanon say they have their work cut out.

They cite overflowing landfills, a polluted coast, quarries gnawing into mountains and state neglect compounding forest fires that hit the country last month before the mass protests began.

Standing on a shack roof near the Bisri Valley, environmental activist Bassam Zeineddine encourages hundreds of fellow hikers who have come to show their support for the dam protest.

"The trees are the only thing left that they haven't taken," he shouts, referring to the country's embattled officials.

"They've left us nothing else -- not water, nor air," rails the member of the "Save the Bisri Valley" movement in a country where the coastline, rivers and air are all polluted.

Protesters clap and cheer, before setting off to march around 20 kilometres (12 miles), walking stick in one hand and billowing Lebanese flag in the other.

Lebanese protesters meditate as they take a break by the ‘Roman Bridge’ during the march in the Bisri Valley. AFP

Along earthen paths they head towards the heart of the valley, singing the national anthem before swiftly reverting to chants from recent anti-graft protests.

"We pay taxes, but their pockets are full!" they intone.

Chronic water shortages

The government says the Bisri dam is vital to tackling chronic water shortages.

But activists say it will ravage most of the region's farmland and historic sites, and they also fear the consequences of building it on a seismic fault line.

Deep in the valley during their hike, the protesters find a cement-making machine.

Yellow diggers also sit idle, after several trucks left the site earlier following recent sit-ins, in what the activists say was a small victory.

Nearby, walkers snap images of uprooted tree stumps.

Roland Nassour, 27, says an ongoing survey of the valley has found several oaks and pines ripped from the soil, but that so far most of the valley's canopy has thankfully been spared.

"The environment is a key part of the revolution," says Nassour, who is also part of the movement to protect the Bisri Valley.