Lake Waahi


General Information

Lake Waahi is the third largest lake in the Waikato Region and has suffered from high levels of suspended sediment entering the lake, originating from both pastoral and mine Drainage. Currently, the lake is considered to be eutrophic. At times 90% of the sediment entering the lake resulted from coal mining. Mine discharge, increased agriculture, clearing of native forest and the resulting increase in nutrient and suspended sediment levels are the primary cause of water quality decline.

Lake Waahi became dominated by exotic macrophytes prior to 1978 and in 1978-79 the macrophyte populations crashed. This was attributed to low lake levels due to low rainfall, high nutrient concentrations and continued sediment input from mining (Dell et al., 1988). Currently Lake Waahi remains unvegetated and is extremely turbid, which renders it undesirable for recreational activities.

Lake Waahi adjoins the Waikato River, but inflows from the river are prevented using a one-way weir, which allows overflow out from the lake. Waahi is separated from the North West arm by a coal haulage road.


Lake Waahi Statistics

Area522 ha
Maximum depth5 m
Trophic stateSuper-eutrophic
CatchmentArea 91.2 km2, pastoral, but has received mining inflows in the past.
RecreationGame bird hunting, boating and fishing (limited by poor water quality).
Restoration progressOne-way weir, to overflow into the Waikato River.
Peat influenceLow-none
Reserve status 
Submerged vegetationNone currently, but has supported populations of the native species: Ealine grattioloides, Utricularia australis, Ruppia polycarpa, Pilularia novae-zelandiae, Isoetes kirkii, Ranunculus limosella, Potamogeton pectinatus, P. ochreatus and P. cheesemanii, Zannichellia palustris, Chara corallina, C. fibrosa, Nitella leptostachys, N. pseudoflabellata and N. hyalina. Introduced species include: Egeria densa, Lagarosiphon major.
Harmful algae 
Invasive fish 


Images


Lake Waahi. Photo taken by Wendy Paul


References

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.

Kirk, T. (1871). Notes on the botany of certain places in the Waikato District. Transcripts of the New Zealand Institute, 3: 142-147.

Dell, P. (1988). Lake Waahi catchment water and soil management plan. Waikato Catchment Board Technical Publication Number 56