The Manuherekia River at Alexandra is once again 'unsuitable' to swim in following test results on January 8, which showed elevated levels of E.coli for the second time in two weeks.

Testing of the river is done every Monday, but results are not received until Wednesday.

The popular Shaky Bridge swimming spot has had a mixed summer with regular water testing of the Manuherekia River showing elevated levels of E.coli on a number of occasions.

On December 27 LAWA (Land Air Water Aotearoa) reported unhealthy levels of bacteria making it unsuitable for swimming, but testing on January 3 showed it was back to good health, however a week later the quality of water had declined again.

Central Otago experienced heavy rainfall on December 24 and 25 and LIWA advised on its website to not swim in rivers two to three days after heavy or prolonged rain - even at sites that have good water quality.

LAWA tests sites around the country weekly from December 1 to March 15 and the Shaky Bridge overall has a ‘poor' long term rating.

The highest E.Coli rating per 100ml value since monitoring began five years ago has been recorded as 2420, with levels over 540 considered high.

From the eight samples this summer, only 50% per cent of the time it was suitable for swimming, 25 per cent of the time caution was advised and 25 per cent it was unsuitable.

LAWA has tracked the source of past bacteria as both ruminant (sheep/cows) and human waste.

The estimated risk of Campylobacter infection from E.coli was common after rainfall, as storm-water and rural run-off may contain human or animal effluent.

Potentially toxic algae can also rapidly bloom to harmful levels, and not all freshwater sites were monitored for it, the site said.

Data from the past five years shows overall the Manuherekia River has been suitable for swimming under the Shaky Bridge 74 per cent of the time, with 18 per cent caution advised and 8 per cent of the time unsuitable.

LAWA also checks Lake Dunstan at Alpha St in Cromwell, the Clyde Rowing Club, the Clutha River/Mata-Au at Dunorling St, Pinders Pond and the Taieri River at Waipiata.

All have received good water quality reports. Check out the section in The Central App under reports, Safe to swim? before you go swimming to be sure the spot is safe.