The river Thames flows through South London and is the longest river in England in its entirety. The river has a long and varied interaction with human history. In the nineteenth century, water quality had deteriorated with industrial advancement and the dirty river water was linked to four cholera outbreaks between 1832 and 1862, killing tens of thousands of people. At the same time, railway bridges were added to road bridges, and commercial and pleasure activities along the river increased. The Thames has long been associated with rowing, and presently there are more than 200 rowing clubs along the river. The University Boat Race between Oxford and Cambridge occurs annually.