At any cave (or in the country in general), if people think that there is a pollution, they should report it to the water companies or else the EA or Natural Resources Wales or Scottish EPA. That will mean that is properly investigated and handled and can lead to a prosecution if necessary. Water companies do prefer it if you tell them first because they can respond more quickly (so reduce the impact).For the Wye, I expect that the main source of pollution is from the fields and industry. There were news stories last year alleging that poultry farms are causing pollution. This re-enforces my point about focusing on water quality: it's the bit that will determine whether you're healthy or sick and finding the source of poor quality water means you can deal with the root cause.
My suggestion was next time you had an incident like this you tipped in a good dose of fluorescein with it. That would bring it to people's attention when the Wye goes green!
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