How quickly things change. Bum-boats used to ply along the Singapore river (it was dirty and stinky back then) as lighters carrying goods to unload onto the godowns along the river bank.
When the port activities move to Tanjong Pagar, a massive clean-up ensued and in the 80s-90s, the bum-boats ply tourists along the now-clean river to enjoy the sights.
Come now, some of these boats serve as river taxis to provide people with alternative means of transport around the city centre. It’s still popular with tourists, but maybe it will be popular among locals again too someday.