Apparently “There’s a simple mnemonic that helps distinguish flotsam from jetsam.
Flotsam (or floatsome) are those items which are floating as a consequence of the action of the sea. 
Jetsam are those which have been jettisoned by a ship’s crew (although that may float too of course).”
(First picture downstream from Abingdon Lock. Second picture the weir pools. The level of the River Thames has been quite high of recent days.)
As a youth in Abingdon, I liked to visit what I think is now called the margaret brown gardens.
at the time, there was a boat port of sorts cut into it – long abandoned.
the part that faced onto the river could only be reached through brambles which, to me at the time made it a secret hideout of sorts – you could sit there for hours in peace. one day, floating in the gunge – and that seemed to attract a lot of gunge and dead fish, there was floating what seemed to be a polystyrene sheet with a raw ready to cook chicken floating on it. for some reason this freaked me out – and I sometimes wonder what I really saw that day.
YUM!
YUK!!!