Lake Ngaroto

General Information

Lake Ngaroto is not directly associated with the encroachment of peat bogs in the Waikato valley, but is instead affected by local wetland development around its margins (Selby & Lowe, 1992; Lowe & Green, 1987). Peat surrounding Lake Ngaroto extends to about 0.5 m deep at the lake margin and down to 2.5 m approximately 600 m from the lake edge. The peat associated with Lake Ngaroto tends to be lake peat, deposited when the lake area was much larger, and sedgy peat, which comprises marginal lake vegetation in a semi-decomposed state (Thompson, 1994).

Lake Ngaroto

Lake Ngaroto photo taken by Wendy Paul

Although the bottom sediments of Lake Ngaroto do not become anoxic in the summer, internal nutrient loading remains important. This occurs because in very productive lakes the sedimentation of organic material in summer is so high bacterial consumption of oxygen reduces the oxic layer of sediment to a few millimetres. Thus the capacity of the sediment to bind phosphorus is reduced and phosphorus is released from decomposed organic matter or deeper parts of the sediment (Søndergaard et al., 2003).

Restoration Action

Lake Ngaroto is used extensively for recreation, although recreational activities often become impaired during the summer months when cyanobacteria reach toxic levels in the lake. Current restoration activities include; placing a weir on the main outflow to regulate water levels, building sediment traps on the main inflows, riparian planting, spraying pest willow species and establishing a fenced reserve margin.

Lake Ngaroto Statistics

Area 108 ha
Maximum depth 4 m
Trophic state Eutrophic
Recreation Primarily yachting and rowing; bylaws prohibit general use of power boats on the lake. Other activities include duck shooting and fishing. The 5 km walking track around the lake is also a very popular use of the reserve.
Restoration progress Lake perimeter is fenced and riparian restoration is underway
Peat influence High, Kainui peat bog
Reserve status Several allotments were classified for recreation reserve, with (the former) Waipa County Council appointed to control and manage them. GZ 1984 p.853, 1975 p.97, 1974 p.328. This appointment transfers to the now Waipa District Council.
Submerged vegetation Submerged vegetation is not common, but marginal species that have been recorded are: Typha orientalis, Nitella hookeri/cristata, Potamogeton ochreatus and P. cheesemanii.
Harmful algae Periodic blooms of harmful algae, primarily Microcystis and Anabaena 
Invasive fish Koi carp, goldfish, Koi carp x goldfish hybrids, catfish, rudd and gambusia

References

Beaton, R., D. Hamilton, M. Brokbartold, C.Brakel, and D. Özkundakci. 2007. Nutrient budget and water balance for Lake Ngaroto. CBER Contract Report No. 54.

Boswell et al. (1985). Waikato small lakes: resource statement. Waikato Valley Authority.

Champion et al. (1993). The Vegetation of the Lower Waikato Lakes. Volume 2: Vegetation of thirty-eight lakes in the lower Waikato. NIWA Ecosystems Publication No.8 August 1993.

Faithfull et al. (2006). Waikato peat lakes sediment nutrient removal scoping exercise. Environment Waikato Technical Report TR06/15.

Hicks et al. (2001) Fish populations of Lake Ngaroto, Waikato, and fish passage at the outlet weir. CBER Contract Report 14.

Paul, W., Özkundakci, D. and Hamilton, D.P. (2008). Modelling of restoration scenarios for Lake Ngaroto. CBER Contract Report No. 81.

Thompson M. (1994). Substrate coring around the Waipa Peat Lakes to aid in the establishment of Esplanade Reserving. BSc (Technology) Industry Report. University of Waikato, Hamilton, New Zealand.

Selby M.J. & Lowe D.J. (1992). The middle Waikato basin and hills. In, J.M. Soons & M.J. Selby (Eds.). Landforms of New Zealand (2nd Ed.). Longman Paul: Auckland.