Aquae Sulis Western Roman Empire and its urban life declined. However, while the great suite of baths fell into disrepair, some use of the hot springs continued. After the end of Roman rule in Britain around AD 410, some residents seem to have remained, but violence seems to have taken root for, in the 440s, a young girl's severed head was thrust into an oven in Abbeygate Street. As far back as Geoffrey of Monmouth, the Arthurian Battle of Mons Badonicus (c. 500) has been suggested to have taken place near Aquae Sulis. In medieval times, the Roman temple at Bath was
Aphanizomenon flos-aquae toxic chemicals released when cells die. Once released (lysed), and ingested, these toxins can damage liver and nerve tissues in mammals. In areas where water quality is not closely monitored, the World Health Organization has assessed toxic algae as a health risk, citing the production of anatoxin-a, saxitoxins, and cylindrospermopsin. Dogs have been reported to have become ill or have fatal reactions after swimming in rivers and lakes containing toxic "A. flos-aquae". Microcystin toxin has been found in all 16 samples of "A. flos-aquae" products sold as food supplements in Germany and Switzerland, originating from Lake Klamath: 10 of 16