Ring EA..0800807060....if there are licensed outputs with consent they will know....if not then they need to know.
THEY will do the running around and checking.....its their job

and they won't be upset even with a false alarm.
When you ring up make sure you are given a reference number as this will give you a guaranteed 'report back'.
A week of watching is too long

.....you could be kicking yourself big time
Did you think of taking a sample of the water yourself.....even a basic look at the water in a milk bottle will indicate whether there are solids in suspension for example.
Sometimes even the smallest sample can be the hinge-pin in finding the culprit of pollution....especially if it goes down a river as a 'plug'.