PERFECT BLUE: Owhiro Bay looks safe.

A POPULAR  Wellington beach that was closed last week with high bacterial contamination has exceeded Environment Ministry safety guidelines repeatedly this summer.

Enterococci bacteria at Owhiro Bay have exceeded the ministry’s most dangerous “action” level on five occasions since summer water quality testing began in November.

Under the guidelines, a bacterial count of more than 140 units per 100ml triggers an alert and follow-up monitoring. When two consecutive samples show levels above 280/100ml, an action response is triggered and the beach is closed to avoid health risk.

Ingesting water contaminated with enterococci bacteria can cause diarrhoea, stomach cramps and vomiting. Cuts and skin lesions can also become infected.

While Greater Wellington Regional Council testers have recorded a number of action readings at Owhiro Bay, on each previous occasion they fell back to safe levels within 24 hours.

Last week, however, they recorded consecutive readings of 372 and 1024 – almost four times action levels – and the beach was closed. 

Regional council water quality scientist Summer Warr says the high readings were almost certainly caused by the previous weekend’s high rainfall. Heavy rains flush out stormwater systems which may be cross-connected with sewers.

She says the Wellington coastline experiences “high energy” pulses of rainfall that can quickly flush stream and stormwater outfalls.

“That’s why we warn people not to swim at [urban] beaches for 48 hours after a heavy rainfall.”

While this warning is issued at the start of the summer bathing season, “the regional council doesn’t have any specific strategy for letting people know”, Ms Warr says.

CONTAMINATION CULPRIT: Waters from Owhiro Stream flow into the bay

She warns that Owhiro Bay seems to be more susceptible to exceeding the guidelines.

“There are definitely other options around Wellington that have reliably lower results – places like Scorching Bay and Princess Bay that have fewer stormwater outfalls.”

Owhiro Bay School principal Karen Hardie says water quality in the area has long been a concern.

Children have been barred from Owhiro Stream, which runs behind the school, after repeated council warnings about possible contamination.

She says she was not aware of the regional council’s warning to avoid beach swimming after heavy rains, but will include the advice in the next school newsletter.

Iqbal Idris, from Wellington City Council’s water management service Capacity, says blocked drains on private land are often to blame for elevated bacterial levels at city beaches.

“The beach closure at Island Bay last month was eventually traced back to a drain at a block of flats 3km away.”

He says the Owhiro Bay catchment stretches as far north as Brooklyn and includes a number of potentially contaminating sites, including landfills.

Engineers are inspecting and replacing drains in the area as part of the council’s long-term sewerage pollution elimination project.

Since the city council began the project in 1993, the quality of fresh water feeding into the sea has dramatically improved, Mr Idris says.

He points to the Overseas Passenger Terminal culvert, which recorded a faecal coliform count of 38,500 cfu (colony-forming units) per 100ml in 1994. Ten years later, after extensive work to the stormwater system, the median level was down to 1,500 cfu/100ml.

He urges the public to do their bit by notifying the council about blocked drains or sewage overflow.