Yeading Walk : Yeading Brook

Work was done earlier in the day to remove sedge from the banks from the stream, so this may have disturbed the bed.
The whole river appears tohave a faint white coating, making it cloudy. Turbitity is 30+(Max reading) however.
Some dead invertebrates found
Medium Flow.
Warm weather

Other species found:
red midge larvae
Aquatic worm
16 water hoglice
18 small leech
1 small fish fry
2 slugs (relocated them to dry land)
Flatworm (Dugesia Lugubris)
2 very large European Fish leech 20cm when stretched out. One escaped from the tray!

People in the park keep telling us about how the river would frequently change colours often 30+ years ago due to the Kodak factory at Headstone disposing of their chemicals in it. It is noticable that the Riverfly results get better the further away from Headstone you go. Could there be some residual damage to invertebrates caused by these chemicals lingering in the environment? Have tests ever been done?
Silver nitrate is one of the chemicals named in the prosessing of paper at the factory, there will be many others too.