Scratch that ....
Go to
Report, view, and discuss local street-related problems.
www.fixmystreet.com
Report the stuff, preferably with a photo.
They report it to the council. Fixmystreet also follows up with the council's and publishes response times, successful conclusions etc so the council takes any report from fixmystreet far more seriously than a direct report to the council or referred from some other government body.
If the waste is less that 10 tonnes then the EA will just pass it onto the council to deal with.
The app is really good. You can upload a photo there and then and pin it on a map. Incidents can be reported in around a minute or so, with your mobile while at the river. Great for reporting flytipping like this.