Lake Whangape is the second largest lake in the Waikato region (Waikare being the first) and is a riverine lake. Lake Whangape is considered to be hyper-eutrophic and regularly suffers from toxic algae blooms. However, Lake Whangape was not always in such a bad state. In 1869 and 1870 the botanist Kirk visited the lake to record submerged plant species. Some of them he identified were in water 2 m deep! Currently Lake Whangape has a secchi depth of < 30 cm (ref.). At the time Kirk visited the lake the catchment was native forest and the lake supported a diverse community of native plant species. Since then water quality has declined remarkably, with the invasive Egeria densa outcompeting native macrophyte species as early as 1921.
In 1982 Lake Whangape was described as having relatively low levels of chlorophyll a and total phosphorus and was concluded to be mesotrophic (Town, 1982). At this stage Egeria densa and Ceratophyllum demersum were well established and before the collapse of macrophytes in 1987 they were recorded as covering more than 95% of the lake bed (Barnes 2002).
Barnes (2002) records lake trophic status in Lake Whangape as improving, most probably due to macrophyte reestablishment following the 1987 collapse. However, lake monitoring between 2002 and 2004 has documented a decline in water quality, with Trophic state worsening from supertrophic to hyper-eutrophic. Macrophyte restoration would be advantageous, but macrophyte growth is likely to crash again due to high external and internal nutrient loads. Consequently, the reduction of these loads through better land use management in the catchment, invasive fish removal and internal nutrient load reductions would be recommended before efforts are made to re-establish macrophyte populations.
|Average depth||1.5 m|
|Maximum depth||3.5 m|
|Catchment||Pastoral, in the past Waahi has recieved coal mine waste. 9.1 km2 of associated wetlands (1982).|
|Recreation||Game bird hunting|
|Restoration progress||Rubble weir to control water levels|
|Reserve status||Wildlife management reserve administered by the Department of Conservation.|
|Submerged vegetation||None currently, but has supported populations of the native species: Isoetes kirkii, Ruppia polycarpa, Ranunculus limosella,Zannichellia palustris, Pilularia novae-zelandiae and Lepilaena bilocularis. In 1958 Egeria densa was dominant, with Elodea canadensis and Myriophyllum triphyllum also present (Champion et al. (1993).|
|Invasive fish||Koi carp, goldfish, cat fish, gambusia.|
Barnes G. (2002). Water quality trends in selected shallow lakes in the Waikato region: 1995-2001. Environment Waikato Technical Report No. 2002/11.
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.
Stephens et al. (2004). Rehabilitation of Lake Waikare: Experimental investigations of the potential benefits of water level Drawdown. Environment Waikato Technical Report 2004/25.
Town J.C. (1982). Lake trophic status and water quality 1982 survey. Waikato Valley Authority Technical Report No. 22.
Kirk, T. (1871). Notes on the botany of certain places in the Waikato District. Transcripts of the New Zealand Institute, 3: 142-147.
Link to the Waikato Regional Council information page