DNA tests have revealed the causes of pollution which has blighted a Norfolk beach for the last two summers.
Bathing water quality has been rated 'poor' off Heacham in 2021 and 2022, while visitors have at times been warned not to swim or gather shellfish.
Environment Agency scientists have been using so-called microbial source tracking analysis - a form of DNA testing - to investigate further.
Officials have now revealed what they have learned so far.
They say tests carried out last summer showed that the local sea bird population was a "significant" factor behind the pollution, but also identified contributions from hooved animals like deer and cattle, as well as dogs and humans.
It said samples were routinely taken between May 15 and September 30 at "designated bathing water points" across the country.
It added: "Depending on the circumstances, some of these samples may be subjected to microbial source tracking analysis."
Anglian Water has a sewage treatment works down a track on Fenway, around a mile inland from the beach.
It discharges into a tributary of the Heacham River before it flows between caravan parks and holiday chalets on its way to its tidal outfall onto the beach.
Anglian Water says it uses UV treatment to clean up water leaving the site meaning it undergoes an extra level of disinfection before it goes back to the river.
“The nearby Heacham River can influence the quality of the water at Heacham," the EA went on.
"This river can be affected by both urban and agricultural sources, and the Environment Agency continues to work with Anglian Water and other stakeholders in the area to seek improvements to the water quality.”
The course of the 10-mile-long river, whose upper reaches are classed as a chalk stream, has narrowed and become overgrown in recent years.
The Norfolk Rivers Trust says there are concerns about abstraction. But wild brown trout can sometimes still be seen upstream of Norfolk Lavender.
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