Swimming restrictions remain in place at Wairoa River after water sample results this morning confirmed E. coli levels in the river are still at four times above safe swimming guidelines.

Hawke's Bay District Health Board medical officer of health Dr Nicholas Jones said the DHB was continuing to work with Wairoa District Council and Hawke's Bay Regional Council to understand what might be contributing to the elevated levels.

"Despite yesterday's storm we know that these readings are not rainfall related so we are working with both councils to further investigate the cause," said Dr Jones.

"Regular water sampling and monitoring will continue and the regional council will also be using a faecal source tracking tool to investigate the likely source, which will further help to narrow our investigation."

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Signage put up by Wairoa District Council warning against swimming in the river would remain in place.

Dr Jones urged people to take notice of the warnings and avoid swimming in the river until further notice.