Kettuvallam — houseboats (literally in Malayalam ‘Kettu’ means “to tie” while ‘vallam’ meaning “boat”) which can carry more than 25 tons — was the most preferred transport option to carry heavy loads and also take people to remotest of villages via backwaters

It is said that the master brain behind building shades over the boats, was that of a British man, who on one of his journeys across the waters suggested this idea to build bamboo roof overhead.

https://touriism.travel.blog/2020/04/12/20