The history of Bath, England is intrinsically linked with the natural hot springs that the city is founded upon. In 43 AD Britain was invaded by the Romans and by 75 AD they had built a religious spa complex on the site, which later developed into a bathing and socializing center called Aquae Sulis, ‘the waters of Sulis’.
The baths are routinely drained and cleaned to prevent too much build-up, but even after a good cleaning the algae forms rapidly, giving the bath water its characteristic green hue.
If my bath was that colour, I’d complain to the water company.
Of course, Matt!