Hiking through the south of La Palma, the site of a significant volcanic eruption in November and December last year though we were walking in an area which last erupted fifty years ago, I asked the guide about the channel we were crossing.
The reply was that it was irrigation water for banana plantations on the south west of the island and that the water source was many miles distant.
Seeing one of the volcano vents in this picture I guess that this part of the water channel had had to be re-built after the earlier eruption.
But it is fun to see how far it wanders, this towards its final destination, usefully before the (very faintly visible) lava inflow into the sea from the 2021 eruption.
Being a fascinated engineer I've had a look on return at Google Earth and it is possible to follow the route of the channel - which I've roughly marked on the above map. Total length perhaps 22-25km when taking into account all the 'wiggles' of the channel as it keeps to the contours in crossing the landscape.
My photos above were taken at the southern most part of the route, the second photo looking north-west towards Las India; we were walking down from Los Canarios to the southern tip of the island, admiring the salt pans there.
And, from the internet, a final photo of water supply in La Palma - looking rather like a sophisticated version of the 'spaghetti networks' we see in other parts of the world - interesting!