The sea could become out of bounds to beach-goers at Norfolk's top resort unless pollution levels in the bathing water are cut, a coastline campaign group has warned.

In the Marine Conservation Society's (MCS) 2011 Good Beach Guide published today, two Great Yarmouth beaches, Yarmouth south and Yarmouth pier, and the one at neighbouring Gorleston have slipped to a basic pass standard for their bathing water quality.

Charity spokesman Clare Fischer warned that under more stringent European water quality standards from 2015, a basic pass could in some cases become a failure.

Monitoring for the new standards would begin next year and if a beach consistently failed to meet the legal limits over the next three years, bathers could be faced with a sign advising them not to enter the water.

While the three beaches have slipped to a basic pass from the highest recommended grade, neighbouring Yarmouth north, Caister and Hemsby have retained their top rating.

And the results show a clean sweep of top ratings across North Norfolk from Sea Palling to Sheringham and across Waveney from Lowestoft to Southwold; Hunstanton's two beaches also reached recommended standard.

To achieve a basic pass, 95pc of samples taken have to conform to a strict limit on the level of human sewage and livestock waste; to reach recommended standard, 100pc of samples have to pass the test. Each beach is tested 20 times during the bathing season from May to September.

Ms Fischer said: 'Yarmouth council should be looking at the results from the Environment Agency and working out what the problem is.'

She said results could be affected by a number of factors from heavy rainfall and combined sewer outflows discharging dilute sewage to agricultural run-off.

Charles Reynolds, Yarmouth council's cabinet member for tourism, highlighted the fact the tests were taken last summer and were affected by the heavy rain from June onwards.He said: 'Tests taken so far this year have been perfect but we are aware of the European directive and will be liaising with the Environment Agency and other agencies to ensure we achieve the right results.'

Karl Read, North Norfolk council's leisure and cultural services manager, described the results as 'extremely good news for the district'. He said: 'Our beaches are not only beautiful, they are also some of the cleanest in the country and the regular crop of Blue Flags shows that they are some of the safest as well.'

stephen.pullinger@archant.co.uk