When Kaipara Kaitiaki iwi, from whose harbour Winstone Aggregates extracts large volumes of sand, expressed concern that quarrying activities were depleting fish and shellfish stocks, a study into the issue was initiated. Recognising that the results might necessitate a rethink of our mining methods, the study in fact indicated that the Kaipara is similar to other harbours where depletion is largely the result of vegetation clearance and stock entering inter-tidal areas such as streams, estuaries and the foreshores. Not only was the stock fouling the waterways, they were also damaging plants that prevent silting.

Winstone Aggregates' recommended solution (which local farmers in other harbours have readily adopted) was to fence waterways.