The Wairoa and Northen coast catchments includes the catchments of Wairoa and the smaller catchments of Whakakī, Nuhaka and Mahia. The catchments include Wairoa River – the biggest river in Hawke’s Bay – as well as the Waiau, Waikaretaheke, Mangaaruhe, Ruakituri, Hangaroa and Mangapoike rivers. These catchments also includes Te Urewera, which was previously a National Park.
The Wairoa and Northern coast catchments are home to many native fish, such as three species of galaxiids (whitebait), four species of bullies, two species of mullet, two species of eels, torrentfish, lamprey, smelt and flounder. Lake Waikaremoana has a landlocked population of koaro, which are part of the whitebait family. The Wairoa Estuary, Mangawhio Lagoon and their connected wetlands are home to many of these fish species, as well as an array of bird and plant life.
The combination of steep hill country, soft sedimentary geology and pastoral and forestry land uses in the catchment mean erosion and sediment generation rates are high, relative to the rest of Hawke’s Bay. Once in a waterway, this sediment can impact ecosystem health, alter the way estuaries function, and cause problems to the animals and plants that live there. The Wairoa estuary shows signs of sediment stress.
Water quality in the catchment is generally good. There are relatively low concentrations of nitrogen and phosphorus, compared to other parts of Hawke’s Bay. The issues are high concentrations of suspended solids and loads, and poor visual clarity.
Where conditions are favourable, such as in stony bottomed streams, some waterways in the catchment have nuisance algae (periphyton) growth due to nutrient inputs, particularly during summer low flows.
Lake Whakakī has some of the poorest water quality of any monitored lake in New Zealand. The shallow lake is muddy and has extreme algal blooms. However, bird surveys around the lake recorded a number of threatened species, fernbirds, bittern and spotless crake. These birds indicate high ecological value and show that ecosystem health is not just about water quality.
The Wairoa River mouth has closed at times due to large swell events and sea currents. This causes low-lying areas near the township to flood. The river mouth is manually opened by HRBC to prevent flooding.
There is a high level of salinity lower down the Wairoa River, which may affect the supply of groundwater.
The following infographic displays what the community has told us about this catchment in our first round of engagement. For more information read the full Kotahi Community Engagement Report here.
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