Just how vile and dangerous the Thames was in Victorian times can't be underplayed though (my mother remains pretty vocal about how terrible it was in the 60s!). The idea of moving Parliament out of London was even considered as the smell from the Thames was affecting daily life as far upstream as Westminster: https://en.wikipedia.org/wiki/Great_Stink

An interesting aside related to the Princess Alice disaster is that the main northern sewer was only finally fully working months before the disaster and its outflow was very close to the crash site. Work began in the next decade to purify the sewage rather than just dumping it into the Thames there.

But I'd argue (and this is just a hunch) that sewage was "deadly" then in the sense that if the water then were as clean as now, the death toll would have been far lower, especially as the crash happened so close to (admittedly rather muddy) land.