The lake is enormous. It is over 190 kilometres long - roughly the distance from London to Manchester - and 280 metres deep in places. Around its shore live the Aymara and Quechua people, whose families have farmed and fished here for thousands of years.
A group called the Uros people had a brilliant idea hundreds of years ago. They learned to build their own islands out of a tough reed called totora that grows in the lake. They cut bundles of reeds, tie them together into thick mats, and lay mat after mat on top until the whole 'island' is strong enough to walk on.
Each floating island is about the size of a small football pitch. Several families live on each one. Their houses, their boats and even some of their fires sit on top of the reed bed. As the bottom rots away in the water, they simply add more reeds on top - so the island stays the right thickness.
The Uros people travel between islands in boats also made of totora reeds. The reeds smell sweet, taste a bit like cucumber if you chew them, and last for ages. There are over 60 floating islands on Lake Titicaca, and children grow up running across spongy reed floors that wobble gently with the lake.