Caution has been advised to swimmers using the Manuherikia River at the Shaky Bridge in Alexandra and at Lake Dunstan near the Clyde Rowing Club after elevated E.Coli levels over the last week.

Land and Water Aotearoa (LAWA) has been testing swimming areas across the region since early December, and readings on December 30 showed both had higher levels of bacteria than normal.

Anything above 250 MPN/100ml was when LAWA issued caution to swimmers, and both swimming spots were last recorded at 350.

This meant the water quality was generally suitable for swimming, however young children, the elderly or those with compromised health may be at increased risk of illness.

Heavy rain flushed contaminants from urban and rural land into waterways and LAWA advised people not to swim for two to three days after - even at sites that generally have good water quality.

Further investigations of the sources of ongoing bacteria in the Manuherikia River during the past year have identified a combination of ruminant (sheep/cows), avian (birds) and human.

Out of the five tests carried out this summer, this was the first time the two swimming spots had recorded elevated levels of E.Coli.

The Lake Hawea swimming spot at the camping ground had been considered unsuitable for swimming between Christmas and New Year, but the Otago Regional Council, who contracted LAWA for the testing, said the source was unknown.

Testing on December 30 showed the swimming inlet at 1000 E.Coli/100ml, with anything above 550 making it unsuitable.

Lake Hawea had an ‘excellent’ long-term grade for water quality, and the latest warning caught many people by surprise, particularly those camping nearby.

On the LAWA website it said that bacterial contamination was common in Lake Hawea after strong winds that stirred up the lake sediment or after heavy rain.

ORC scientist of water quality Helen Trotter said this week’s result at Lake Dunstan was back at the typically low levels for that site (1MPN/100ml).

The Manuherekia at Shaky Bridge was also back down to just 179 MPN/100 mL which met the ‘suitable for swimming’ threshold again.

Summer monitoring results showed the site was suitable for swimming about 73 per cent of the time (based on the past five years). 

Slightly elevated E.coli levels were relatively common at the Shaky Bridge, with 20 per cent of results in the past five summers in the ‘amber/caution advised’ category and 7 per cent at ‘red/unsuitable for swimming’ levels. 

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