"art" wrote in message
oups.com...
snip
In the middle of the 19 century the River Thames which is a tidal
river
froze over in London. The ice was so thick that a fair was held on the
ice.
If I remember correctly water height varies about 13 feet due to tide
change
so you can imagine how thick the ice was to hold the tides back.


The ice was 5 feet thick and the river flow was severely obstructed by
numerous bridge butresses. The River Thames was so polluted that it was more
like liquid mud (actually sewage) than water. The river is now so clean that
salmon have been caught swimming in it and the flow is fast enough to
prevent a recurrance of the freezing process that allowed the frost fairs to
take place. Tidal flow is only rarely interrupted by the Thames Barrier to
prevent exceptionally high tidal surges from breaching the river defences in
Central London.

Mike G0ULI