Regional lakes
Lake Wainamu
On this page:
- About Lake Wainamu
- How did this lake form?
- How healthy is Lake Wainamu?
- Threats to Lake Wainamu
- What is the ARC doing?
- Technical Publications
About Lake Wainamu
Easterly aerial view of Lake Wainamu
Three streams provide most of the water flow into the lake. One of thesepours over the Waitohi Falls at the head of the lake. Another stream flows out of the lake at the north-western end but tends to dry up in summer. The valley here is filled by a huge amount of loose dark sand.
The surrounding steep hills are mostly covered by native forest. There is a small amount of pastureland on the northern side of the lake.
Pied shag, little shag, black swan, and duck can often be seen on the lake. Australasian bittern and North Island fernbird also live around the lake. Native freshwater fish in the lake include banded kokopu, inanga, common smelt, common bully, grey mullet, longfinned and shortfinned eel.
Exotic fish recorded at the lake include catfish, perch, rudd, tench, and goldfish.
Lake Wainamu lies within the Auckland Centennial Park and is a popular recreation spot. Dogs are not permitted at the lake.
Facts
| Location guide | Close to Te Henga (Bethells Beach) along the west coast of the North Island of New Zealand. See a location map of Lake Wainamu. |
| Surface area | About 14 hectares |
| Maximum depth | About 15m |
| Catchment area | About 480 hectares |
| Type of catchment | Pasture (4%) Exotic forest (none) Native forest/scrub (96%) Urban (none) |
| Surface water temperature | Average 17.9°C |
| Number of sampling sites | One site, but water samples are collected at two different depths. |
How did this lake form?
Lake Wainamu formed during past 6500 years, when the Wainamu Stream Valley was dammed by huge dunes of dark iron sand that were slowly blown inland by the prevailing wind.
The existing dunes are still moving slowly into the lake but the dune stabilization programmes along the coast have stopped the supply of more sand.
How healthy is Lake Wainamu?
Since 1998, the quality of the lake water has been monitored as part of our State of the Environment (SoE) Lake Water Quality monitoring programme.
The quality of any lake water is shown by its trophic state. In 2005 the water quality of Lake Wainamu declined to a eutrophic state (green and murky, with higher amounts of nutrients and algae). Before 2005 it was mesotrophic (low to moderate amounts of nutrients and algae).
| Microptrophic | Oligotrophic | Mesotrophic | Eutrophic | Supertrophic | Hypertrophic | |
| 2006/07 | x |
| ||||
| 2005/06 | x |
Threats to Lake Wainamu
Decline in water quality
A sudden and progressive decline in the water quality at Lake Wainamu was already causing public concern by 1996. This was thought to be due to exotic fish that were accelerating the collapse of the submerged aquatic plant community in the lake.
In 2000, observations showed that most of the submerged aquatic plants in the lake had disappeared.
In response, the ARC removed over 9000 exotic fish (particularly perch, goldfish and rudd) between 2004 and 2007.
The water clarity and the growth of submerged aquatic plants have both since improved, although it is too early to link this directly to the removal of the fish.
Invasive pest plants
In 2005, the improved water clarity meant that many submerged aquatic plants, including the invasive pest plants, had shown a substantial recovery compared to previous years.
Egeria was the most widespread of all the submerged aquatic pest plants. In 2005 it formed a dense narrow band outside the reed beds, extending out to a maximum water depth of 4.8m.
What is the ARC doing?
- In 2005 the ARC contracted NIWA to assess the condition of the submerged aquatic plant community in the lake following the removal of thousands of exotic fish, and report the findings.
- In 2006, the ARC commissioned NIWA to help develop a regional management plan for freshwater weeds and fish.
- The water quality is sampled once every two months as part of our State of the Environment (SoE) Lake Water Quality monitoring programme. Find out more about the Lake Water Quality monitoring programme.
- The ARC has operated and promoted the Environmental Initiatives Fund (EIF) since 1999. This support individuals and groups to improve and care for the region's natural, cultural and physical environments. Around $500,000 is available annually. Find out more about EIF.
- We are working with the Department of Conservation (DoC) to support Weedbusters. This is a small-scale initiative fund for individuals or groups that want to eliminate pest plants. The funding helps to cover the cost of tools, herbicides, mulcher hire, greenwaste disposal and promotional activities. Find out more about Weedbusters.
- Since 2004, the ARC has had a programme of pest fish control in place.
Technical Publications
The ARC has a number of technical publications relating to this subject. Follow this link to see the full list of ARC technical publications.
