Changing weather conditions has been affecting some of Central Otago’s swimming spots, with two Alexandra rivers considered unsuitable for bathers last week, but now back to being safe again.

The Manuherikia River at the popular Shaky Bridge was prone to changing levels of E.Coli after high rainfall, but last week the Clutha River at the Dunorling Street boat ramp was also affected.

Testing from Land, Air, Water Aotearoa (LAWA), on January 27 showed 1300/100ml of E.coli, at the Shaky Bridge and 649/100ml at the Clutha River swimming spot.

But further testing three days later found E.coli levels had returned to normal (low levels).

Otago Regional Council scientist, water quality Helen Trotter said widespread rain prior to sample collection last Monday resulted in high bacteria results at several monitored recreation sites across the region.

This was the fourth summer Clutha River at Dunorling St had been included in the recreational water quality programme, and only the second instance of a red alert level result. 

The other was on March 6, 2023 (also 649 MPN/100 mL) and that result was also associated with rainfall, she said.

Faecal indicator bacteria (E. coli) could be introduced to the environment through animal and bird droppings, effluent and waste water discharges, and run-off from rural land and stormwater.

“These results are an excellent example of why it is advised to avoid swimming for at least 48 hrs after heavy rain.”

The highest reading at the Shaky Bridge has been 2420/100ml - once in 2020 and again in 2022.

More information about recreational water quality can be found at LAWA

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