I just received the following correspondence that I felt was worth including here as-is:
I thought Reading Naturalists might be interested in my observation (see the attached photos, I took this Saturday and Sunday) of freshwater sponge (Porifera, family Spongillidae) right under the bridge of Reading – red arrow points to the place in the attached image. It seems that there are at least 2 species under the bridge and these probably are Ephydatia muelleri (the massive ones as in IMG_2649s.jpg) and Spongilla lacustris (the ones shaped like fingers as in IMG_2662s.jpg). One of the colonies grows on submerged Tesco cart under the small bridge construction below the Reading bridge.
Anyway, their presence should probably indicate the quality of Thames water is not so bad :-).