Health risks are expected at some of our most popular West Coast beaches this summer but efforts are being made to get on top of the problem.

The popular fresh-water lagoons at Piha (north and south), Karekare and Bethells have shown some of the region's poorest water quality during more than 10 years of monitoring.

Public health warnings have regularly been posted amid fears the water is contaminated by leaking septic tanks. Cows, ducks and dogs have added to the risk of infection caused by faecal matter.

"The water is not clean enough. It's a really bad look, but it's not an overnight fix. It's going to take a whole-of-community response," said Piha resident Sandra Coney, who chairs the Waitakere Ranges Local Board.

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Three-quarters of the 63 beaches, four lagoons, one stream and one lake tested for water quality in Auckland last summer were safe for swimming, but the number of sites and days with health warnings were significantly higher than the previous two years.

A total of 22 sites over 183 days received health warnings, compared with 18 sites and 96 days in the 2013-2014 summer and 16 sites and 124 days the previous year.

Lagoons are not the only swimming spots with water-quality issues in West Auckland.

Laingholm, Wood Bay, Fosters Bay, Huia, Cornwallis and Te Atatu were occasionally declared unsafe for swimming and issued with health warnings.

North Shore and city beaches had fewer issues, with Milford and Milford south, Narrow Neck and Judges Bay among those issued with health warnings after two consecutive water tests exceeding the microbiological guidelines set by the Ministry for the Environment and Ministry of Health.

Phil Brown, the council officer leading the West Coast lagoons project, said the problems with on-site wastewater systems were complex.

He said it only took a dozen people to come down to a bach on Christmas Day, use the toilet, shower and wash towels for a septic tank to fail.

"You will have raw wastewater running over the ground that gets into the stream that gets into the lagoon."

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Old septic tanks, made for when people came over summer without dishwashers or flush toilets, have become overloaded as more baches have become fulltime homes or replaced with larger houses.

Cows having access to streams at Bethells Beach is another contributor. The council has begun offering subsidies to farmers to fence streams.

Mr Brown said nine council departments were working under myriad rules and legislation on an action plan to deal with the pollution. It would be a long game of five to 10 years, he said, working with the community to fix the problem.

The project had many strands, including waiving resource consent fees to upgrade septic tanks, requiring people to upgrade tanks not working properly and the possibility of a council-backed scheme to pay for new tanks through rates.

New tanks typically cost more than $20,000.

The council has contracted EcoMatters Trust to work with the community to raise awareness and offer free septic tank inspections.

"We can reduce the levels of contamination. Because lagoons are challenging environments we are not going to make this crystal-clear Great Barrier water quality but certainly we can improve it from its current state."

Ms Coney said it would be several years before the problems were solved, but a great deal had already been done. At Piha, the surf club, the Returned and Services Association and camp ground systems had all been upgraded. Last year, scientists used DNA tracking techniques to identify the source of pollution at Piha and other lagoons.

This year's safeswim programme runs from November 1 until March 31.

Solving water-quality issues around popular West Coast lagoons is not an overnight fix

Dirty beaches Health warning days

53

-- Piha south lagoon

29 -- Bethells lagoon

23 -- Piha north lagoon

18 -- Karekare lagoon

17 -- Karekare carpark

6 -- Laingholm beach

4 -- Fosters Bay

4 -- Herne Bay beach

4 -- Wood Bay

4 -- Milford south beach

3 -- Huia beach

2 -- Narrow Neck beach

2 -- Judges Bay

2 -- Green Bay

2 -- Takapuna beach

2 -- Clarks beach

2 -- Stanmore Bay

2 -- Mellons Bay

1 -- Armour Bay

1 -- Cornwallis beach

1 -- Te Atatu beach

1 -- Milford beach

Source: Auckland Council 2014-2015 summer season

For summer beach info go to www.aucklandcouncil.govt.nz