Kai Iwi Lakes Reserve

The Kai Iwi Lakes are situated approximately 35 kilometers northwest of Dargaville, a small town in Northland, New Zealand. Taharoa Domain covers an area of about 538 hectares[4] and is characterized by a combination of sand dunes, native bushland, and the three interconnected lakes. The lakes themselves are unique in their formation, with each one occupying a basin formed by windblown sand.[5]

The catchments surrounding these lakes are predominantly covered by high-producing exotic grassland pasture, exotic pine forests, and manuka/kanuka scrubland. Some areas have a mixture of different vegetation covers. The lakes' surface areas, catchment areas (including the lakes), and volumes are as follows: Kai Iwi – 22.6 hectares, 120.9 hectares, and 1.43 million cubic meters; Taharoa – 197 hectares, 439.4 hectares, and 25.18 million cubic meters; Waikare – 26.5 hectares, 149.5 hectares, and 2.97 million cubic meters.[6]

During the warmer months, each of the lakes experiences thermal stratification. According to the National Policy Statement for Freshwater Management, the phytoplankton (chlorophyll-a) status for each lake is as follows: Kai Iwi teeters between states A and B, leaning more toward state B; Taharoa generally remains in state A, occasionally entering state B during small periodic events and returning to state A afterward; Waikare is more similar to Kai Iwi than Taharoa, occasionally crossing into or verging on state C and recently favouring state B.

Nitrogen levels in Lake Kai Iwi have occasionally reached state C,[7] but they tend to revert back to state B. Taharoa generally maintains a high state A for nitrogen, while Waikare consistently remains in state B. Phosphorus and toxic ammonia levels for each lake are categorized as state A.

Kai Iwi has historically been classified as low mesotrophic and has recently improved, entering the oligotrophic range. Taharoa is categorized as low oligotrophic (indicating good water quality) and can reach the microtrophic range (very good water quality). Lake Waikare is considered medium oligotrophic (also indicating good water quality).

There is limited climate data for the Kai Iwi lakes but estimates can be made from nearby climate stations. The average air temperature in Dargaville is 15.3°C, ranging from 11.3°C in July to 19.8°C in February. There is unlikely to be much difference in air temperature between Kai iwi Lakes and Dargaville. DOC (2011) reported the average annual rainfall at the Maitahi Wetland Scientific Reserve, just south of the Kai Iwi Lakes is about 1500 mm. This and recent rainfall data near Kai Iwi Lakes, suggests that average annual rainfall at Kai Iwi lakes is about 1,400 mm with the driest months being November to February and the wettest months being June and July. This is consistent with historical rainfall data from Kai Iwi lakes. Historical average annual rainfall for Kai iwi Lakes includes 1,297 mm based on an 18 year record at Fanning rainfall station (McLellan 1985) and 1,226 mm at McLeods at Kai Iwi based on data from 1986 to 1993. Average annual open water evaporation in Dargaville is 1,018 mm, with the highest evaporation rates in December and January and the lowest in June and July.[6][8]

1. Lake Taharoa: The largest and deepest of the three lakes, Lake Taharoa stretches across approximately 57 hectares. It is a popular spot for swimming, kayaking, and water sports. Lake Taharoa exhibits complex bathymetry, featuring a deep central basin of 38.8 meters[9] connected to two shallower basins, as well as a discrete nearly closed basin at its western end and some gently sloping beaches. The presence of numerous steep drop-offs limits the development of a littoral fringe with emergent plants. The mean depth of Lake Taharoa is 16.42 meters. Lake Taharoa has been recognised as ‘probably the best example of a clear-water lake in Northland with the deepest recorded (24m) submerged vegetation in Northland’.[3]
2. Lake Kai Iwi: Located adjacent to Lake Taharoa, Lake Kai Iwi is slightly smaller, spanning around 44 hectares. Lake Kai Iwi is a single basin lake with a maximum depth of 15.65 meters[9] and an average depth of 8.15 meters. The northeastern area of the lake is characterized by dense emergent plant growth, which plays a significant role in filtering nutrients from the catchment area.
3. Lake Waikare: The smallest of the three lakes, Lake Waikare covers approximately 8 hectares. It is separated from Lake Taharoa and Lake Kai Iwi by sand dunes and can be accessed via a short walk. Lake Waikare consists of three basins, with the central basin being the deepest at 29.48 meters[9] and an average depth of 10.95 meters across the lake. The shoreline of Lake Waikare undulates, with steep drop-offs on the western side and more gradual slopes on the eastern side of each arm. The eastern edges of the lake are more favorable for the growth of littoral emergent plant communities.[6]

The lakes' clear waters and sandy beaches are popular for swimming and cooling off during the summer months. Visitors engage in water sports such as kayaking, paddleboarding, boating, and water skiing on Lake Taharoa. Fishing enthusiasts catch freshwater species such as rainbow trout, brown trout, and perch in the lakes. The reserve features several walking tracks and trails that wind through the surrounding forests, offering scenic views and opportunities for birdwatching. There are campsites and designated picnic areas with facilities, including BBQ pits and picnic tables. Visitors explore the native bushland, observe birdlife, and view the natural beauty of the area.

https://ref.coastalrestorationtrust.org.nz/site/assets/files/11554/tdrmp_2016_final_20092016.pdf