A new water storage reservoir near Kaikohe is due to start filling in July, weather permitting.
Once complete, Matawii Dam at Ngāwhā will cover 18ha and have a volume equivalent to 300 Olympic swimming pools.
It is one of four significant projects by Te Tai Tokerau Water Trust (TTTWT) in the Mid North and Kaipara.
Regional Economic Development Minister Stuart Nash paid a visit to the construction site on Wednesday, along with local MPs Kelvin Davis and Willow-Jean Prime, TTTWT trustees and officials from Kānoa, the government agency that now administers the Provincial Growth Fund.
The idea is that the dam will store winter rain and allow the fertile soils around Kaikohe to be used for high-value horticulture.
Limited groundwater and a lack of major waterways in the area — plus increasingly common summer droughts — have held back horticultural development in the past.
TTTWT chairman Murray McCully, a former National MP, said the total cost of the project was around $14 million.
Of that, $10m had been covered by a loan from Kānoa, which would have to be paid back to the Government, while the trust was raising the remaining $4m. Information would be sent to potential shareholders in the next few months.
Work to build up the earth dam itself was underway and expected to be finished in three months' time, weather depending.
Dam engineer Eli Maynard, of Riley Consultants, said the 750,000 cu m reservoir would be about one-third filled naturally from its own catchment, while the remaining two-thirds would be pumped from Kaikohe's Wairoro Stream when the water level was high in winter.
The exact split would depend on rainfall.
It could take more than a year to fill completely, he said.
The dam is being built by Map Projects, which also built the flood-retention Kotuku Dam in Whangārei.
Matawii Dam was the first project in the country to be granted fast-track approval under the Covid-19 Recovery (Fast-track consenting) Act.
It will supply horticulture operations such as the Kaikohe Berryfruit venture at Ngāwhā — a partnership between Maungatapere Berries, Ngāpuhi Asset Holding Company and Far North Holdings — and the under-construction Ngāwhā Innovation and Enterprise Park.
McCully said the trust was waiting to find out whether the proposed Otawere Dam, near Waimate North, could go through the fast-track consent process.
That decision was expected in June.
TTTWT was not going ahead at this time with the much bigger Te Ruaotehauhau Dam, which had been proposed near Ōhaeawai with a capacity of 1.4 million cu m.
The trust had money to build one more project in the Mid North and Otawere was the more attractive prospect.
There had also been concerns from Ōhaeawai residents about Te Ruaotehauhau.
Meanwhile, stage 1 of the Redhill Dam, near Glinks Gully in the Kaipara, was nearing completion. Lining of the 270,000 cu m reservoir had started, McCully said.
Resource consent for stage 2 of the Redhill project, which would expand it to a much larger 3.2 million cu m, had been granted. It was due to be built next summer, he said.
In total, TTTWT received $68m from the PGF to fund the water storage projects. Of that, $8.5m is in the form of a grant while the rest is a loan.
Matawii Dam has also been touted as a potential solution for Kaikohe town's regular summer water shortages but that would require the construction of new infrastructure such as pipelines.
It's not yet clear if Matawii will be accessible to the public for recreational use.