Two women row a canoe made of driftwood across a lake, their eyes fixed on a destination in the distance. The woman in the foreground bites her bottom lip with determination. There's a steeliness in her expression that says she's done this many times before.

In a series of exceptional photographs, Italian photographer Luca Locatelli spent a month documenting the lives of the Mosuo tribe, often described as one of the last matriarchal societies in the world. Locatelli travelled to Lugu Lake in southwest China, 2,700 metres above sea level, taking two days to reach his destination by road. There, in a valley on the border of the Yunnan and Sichuan provinces, he shadowed a society where women are in charge and where there are no words to express the concepts of "father" or "husband".

Locatelli describes Lugu Lake as "paradise". "The water is clear and clean and the surroundings are peaceful and beautiful – it's perfect," he says. Known as the "Kingdom of Women" throughout China, 40,000 Mosuo people live in a series of villages around the lake. Women here make most major decisions; they control household finances, have the rightful ownership of land and houses, and full rights to the children born to them – quite radical considering that many parts of China still practise arranged marriages – although political power tends to rest with the men (making the description "matrilineal" more accurate).

But what makes the Mosuo unique is their practice of zuo hun, or "walking marriage". From the age of 13, after being initiated, females may choose to take lovers from men within the tribe, having as many or as few as they please over their lifetime. Male companions are known as axias and spend their days carrying out jobs such as fishing and animal rearing, and visit the women's homes at night, often secretly; any resulting children are raised by the woman's family. The father and all adult men are known as "uncles" – there is no stigma attached to not knowing who a child's father is.

As commerce tries to elbow tradition out of the way and younger generations of the Mosuo are tempted by outside influence, a darker, seedier side has emerged in recent years. Tourism is booming, and the Chinese government is keen to market and monetise the Mosuo to Chinese tourists, even installing a toll booth charging $5 to enter the area from the newly laid main road. Curious and frisky visitors are lured in by the suggestion that the Mosuo women offer free sex – hotels, restaurants, casinos and karaoke bars have been built, and sex workers shipped over from Thailand dress in Mosuo traditional dress in the "capital village", Luoshu.

"Arriving in Luoshu was a shock – it was tacky and not how I expected," says Locatelli. "There were a lot of people asking for money: bar owners and prostitutes that are obviously not Mosuo – it's all geared towards male Chinese tourists."

After talking to locals, Locatelli decided to move on to another village, Lige, in search of "real Mosuo". "I crossed the lake to another village and found them living in the same traditions they have done for 2,000 years – the people there were lovely, kind and living simple, happy lives." With all the modern temptations for the younger generation of Mosuo now right on their doorstep, Locatelli found a community caught between cultural tradition and the modern world.

"Their way of life is slowly changing, but there is a real sense of pride in the way they live," he says. "Men and women are very much equals, but the women are just a little more in charge."