I thought I might make a pitch for the "bad mother of SE1" award.
I let my kids swim in the Thames, in Battersea, during the summer.
According to my friend who lives on a houseboat and whose family regulalry swim, it is best to wait till high tide. There is a 20 minute spell when the water is quite calm. The real threat is driftwood which can go up and down the river at some speed. It is dangerous (says the boat owner) to jump in when the tide is going out as there are a limited number of places where you can scramble out.
I am pretty sure it would not be safe to swim anywhere near a bridge or where there were potential currents. And you need to be very careful about boats, especially those that create a big wash. The bit the kids swam in, oposite Chelsea Harbour, is pretty calm, there were a couple of life belts out as well as ropes conecting the boat, and the kids are good swimmers and stayed near the boat.
As a child we used to swim up near Hampton. And my aunt won some big Thames race around Deptford. I recently saw adverts for quite a long swimming race somewhere around Hammersmith. But for adults not children to my daughter's diappointment.
Perhaps this confession will drag up some comments from the "no children in restaurants" brigade.
Your right Sarah as I have rambled on before on this thread, I swam when the Thames was considered filthy in the fifties, I'm still here, did not get any weird disease...and was cheaper than the baths when you had no money 'cos it was free!
Do people still moan about children in a restaurant? I personally would moan about the behaviour of some adults after a few glasses of wine in restaurants, them I mean not me!