Some members have commented in their catch returns about the brown algae or gunk evident on the river floor over the last month. Professor Nick Goddard, one of our longest standing members commented that it appears each year. The low flow this spring may have made it more evident. Another member, Ken Plume, decided to do some research:-
“I have been involved in freshwater ecology up and down the country for a number of years and never seen this before. I did a search on the internet to try to identify the gunge I came across a paper by a prominent ecologist who had found similar deposits in various rivers. He found that the rocks along the river were inhabited by bacteria that lived off minerals in the rocks the main mineral being iron. As these die they are swept away by the flow but in low water conditions they clump together and sink as the iron mineral in their bodies combines with oxygen in the water it turns into a kind of “semi liquid rust”, his words not mine. I then did a search for medieval iron works in Kent and found the Weald of Kent and Sussex were hot spots with several large iron works on rivers. I don't think the similarities are just coincidence I think it is a realistic answer as to what the stuff is. It isn't toxic as such and should flush away.”
You can read a bit more about this on Wikipedia ('Iron-oxidising bacteria'), if you really want to.
Anyone got alternate theories?