Testing of the River Stour in Christchurch revealed a huge jump in bacteria levels in mid-August.
The teenagers were attempting the record to raise awareness about the UK's sewage issues.
Dozens of people contacted BBC Wales following coverage of Sheen's investigation into chemical giant Monsanto.
An environmental group reports E. coli readings have "spiked alarmingly" in Dorset.
One scientist says there are thousands of sites across the UK that need investigating.
Gallos Brook Community Group says it has carried out more than 14 tests near RAF Upper Heyford.
The tradition on a Carmarthenshire river once fished by US President Jimmy Carter could be coming to an end.
Rescuers say they have found at least five birds with botulism around a man-made lake in Bristol.
The foam was left-over "run-off" from the foam firefighters used to tackle a large blaze on Sunday.
