A levada is like a river, but it's not for boats or for swimming. It's made by people, who build walls to guide the water down the side of a mountain or through a valley. In Madeira, which is a small island in Portugal, there are many levadas.
The people who live on Madeira need water to grow crops and to drink, but there aren't many rivers on the island. So they made levadas to collect water when it rains and then carry it through pipes and channels to where it's needed.
People also like to walk along the levadas because they are usually flat and go through beautiful landscapes. Sometimes the water in the levada makes a waterfall, which is very pretty to see.
But it's important to be careful around levadas because they are slippery and the water can be deep. It's always a good idea to walk with a grown-up and wear shoes with good grip.