DANGEROUS surf conditions can prompt some people to seek a summer cool down further inland, but regular testing has revealed not all water holes on the Northern Rivers are safe to swim in.

Some, particularly closed systems, are more prone than others to build-ups of bacteria, blue green algae and high levels of acidity.

New water tests of the cobalt blue Bexhill quarry revealed the pH is 4.11, less acidic than previous years but still well below safe swimming guidelines.

Southern Cross University Environmental Analysis Lab director Graham Lancaster took a sample of water from the quarry on Thursday.

"There is some acidity issues, but it is getting less acidic with time," he said.

"It still would be outside the swimming guidelines for acidity."

Mr Lancaster said high levels of acidity in water could cause eye and ear problems for swimmers.

In 2002 tests revealed the water's pH level was almost as acidic as vinegar with aluminium levels 2500 times greater than the Australian guidelines.

Then in 2010 tests revealed the levels had dropped from the previous results to about 3.98, which is still well below the National Health and Medical Research Council recreational guidelines for safe pH levels of between 6.5 and 8.5.

Mr Lancaster said both the Evans Head green and blue pools had algae and bacteria issues due to high usage and closed water systems.

"There's a lot of people out there in summer so there are a fair few nutrients that come from that and being a closed system, there's nowhere for the nutrients to go, so they just recycle algae in those areas," he said.

Mr Lancaster said Byron Bay's The Island Quarry was a closed system that experienced similar levels of bacteria and algae.

"Basically a build-up of bacteria, faecal coliform, the indicator of bacteria, can lead to some illness, diarrhoea and gut incidents," he said.

Popular swimming spots like Lake Ainsworth at Lennox Head and Shaws Bay in Ballina were generally fine to swim in, except after heavy rainfall when contaminants, road run-off and faecal matter was washed into the system.

Mr Lancaster said Ballina Shire Council had put several measures in place in recent years to improve the water quality and prevent the build-up of blue-green algae.

"It's just a build-up of phosphorous and really hot weather can bring on the blue green but they monitor it regularly," he said.


Signage is put in place at Lake Ainsworth when enough algae is present to effect the water quality.

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