Most properties at Llangrannog are connected to private drains

But the popular Llangrannog in Ceredigion is one of nine in the UK to have failed to make the grade.

Environment Agency Wales said its investigation into the problems at the beach in Cardigan Bay was now "well under way".

Of Wales' 78 bathing water areas, 72 reached the strictest standards of water quality.

Another five beaches met the minimum EU levels.

Pembrokeshire's beaches reached the highest levels of bathing water quality for the third year running according to the results of sampling taken in the 2003 bathing season.

In north Wales, Prestatyn reached the highest standards of water quality for the first time and Llandudno's two beaches for the second year running.

Llandudno hit the highest water standards for the second year running

In south Wales, all Gower's beaches meet the highest standards, as well as Porthcawl's.

Environment Agency officials have been looking at sources of pollution at Llangrannog, including visiting farm,s and are now concentrating on local sewage systems.

Harmless dyes have been poured down toilets to test sewage systems and investigations, which began late last year, should be completed later this month.

The agency has identified a number of possible sources of sewage and slurry discharge, which it says can both contribute to very high concentrations of bacteria on the beach.

Investigations so far suggest that the main sources of bacteria come from the upper part of the catchment in the Pontgarreg area.

Jan Royall, head of the European Commission in Wales, said: "Setting stringent standards on the quality of bathing water drastically reduces the risk of illness caused by swimming in polluted waters.

"That Wales is meeting, and in many cases exceeding, these standards is good news for parents taking young children to the seaside."

The survey was carried out in the 2003 bathing season and found a UK average of 98.4% compliance - which was highest in Northern Ireland, where all beaches met the grade.

In Wales it was 98.7% and it was 94.8% in Scotland.