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
| Area | 522 ha |
| Maximum depth | 5 m |
| Trophic state | Super-eutrophic |
| Catchment | Area 91.2 km2, pastoral, but has received mining inflows in the past. |
| Recreation | Game bird hunting, boating and fishing (limited by poor water quality). |
| Restoration progress | One-way weir, to overflow into the Waikato River. |
| Peat influence | Low-none |
| Reserve status | |
| Submerged vegetation | None 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
