on a certain stretch of the Thames it is called the ISIS.Why?

Answer 1

The part of the Thames running through Oxford is often given the name the River Isis, although historically, and especially in Victorian times, gazetteers and cartographers insisted that the entire river was correctly named the River Isis from its source until Dorchester-on-Thames. Only at this point, where the river meets the River Thame and becomes the "Thame-isis" (subsequently abbreviated to Thames) should it be so-called; current Ordnance Survey maps still label the Thames as "River Thames or Isis" until Dorchester. However since the early 20th century, this distinction has been lost in common usage outside Oxford, and some historians suggest the name Isis—although possibly named after the Egyptian goddess of that name—is nothing more than a contraction of Tamesis, the Latin (or pre-Roman Celtic)name for the Thames.

Answer 2

The roman name for the thames was thamisis. Whilst most of the thames is now known as the Thames the Oxford section is still known as the River Isis from its Roman name.
Isis was also the Egyptian Goddess for Women and Magical Powers. She was married to Osiris and accompanied poeple through the underworld. Maybe this is where the Romans got the name?

My daughter's name is Isis
Joanne

Answer 3

Not a certain stretch.
On a specific stretch at Oxford it is called the ISIS.
The term is believed to be a contraction of Tamesis, the Latin (or pre-Roman Celtic) name for the Thames, and is especially used in the context of rowing at the University of Oxford.

Answer 4

Lots of rivers change their names at certain points along their route, such as when they join other rivers