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Lake Alexandrina is located in the Mackenzie Basin of New Zealand's South Island, between the much larger lakes of Tekapo and Pukaki, to the north of Lake Tekapo township. The lake is spring fed with an outlet on its eastern shore mid way down the lake. The outlet feeds into a smaller lake, Lake MacGregor before feeding into Lake Tekapo described as “Opaque and milky blue” in colour. In the desert terrain of the Mackenzie Plains, Lake Alexandrina is considered as an “oasis of life”.It is a shallow lake with distinct indications of glacial origin.

Lake Alexandrina is a nature reserve and a trout fisherman's paradise; salmons are also reported. It offers splendid fishing opportunities, particularly for trout fishing, brown and rainbow trout species. A small number of fisherman's huts are clustered at each end of the lake and near the outlet. Row boats are the only mode of transport on the lake as Sail and motor boats are prohibited.

The Maori name for the lake is Whakatukumoana.

Geography
Categorized as a Canterbury High County lake in the Mackenzie Basin, it lies at short distance from Lake Tekapo and is approached from the State Highway 8 via the Godley Peaks Road. The lake covers an area of 640 ha with width of 0.9 km and extending to a length of 7.2 km. Its shores are flat. The maximum water depth in the lake is reported to be 27m. The catchment of the lake has landscape which has good wildlife but also has extensive cultivation which brings in lot of nutrients into the lake, enriching its phosphorous content.

The lake's annual water resources have been assessed as contributed from surface streams: 5.72 Mcumces (27%), overland flows: 1.11 Mcumces (5%), ground water sources: 10.1 Mcumces (48%) and from precipitation: 4.11Mcumces (20%). The storage in the lake lasts four years.

Only row boats are permitted to operate in the lake waters.

Chemical properties
The lake has been classified as mestrophic type. Chlorophyll levels of 0.4-3.8 mg/1 have recorded during observations carried out between November 1978 and March 1979. The total phosphorus at 1 m depth was 0.009-0.015 mg/l as measured in March 1979. The reasons attributed to high nutrient content and consequent high degree of phosphorous levels are due to nutriens netring from the lake catchment, underground sources, grazing on the periphery of the lake, human habitations around the lake, aerial spray and stocking in the trout-spawning streams.

Threats
The threats to the lake waters that were identified in the 1980 were, regular occurrence of algal (Anabaena) blooms which were a result of high nutrient levels of phosphorous, survival of wildlife and recreational fishery. It was assessed by measurements that nearly 50 percent of the phosphorus was contributed by groundwater with 32 percent from surface water inflows and only 3-9 percent from hut settlements. This resulted in poor quality of the lake waters and as a result measures to check the phosphorus content in the lake received priority attention of the Government of New Zealand.

Conservation measures
In order to take adequate remedial measures to check the inflow of nutrients into the lake which had raised the phosphorous content in the lake waters to unacceptable levels, in 1984, The Lake Alexandrina Steering Committee was set up which identified the problem area causing deterioration of water quality due to phosphorus as from the hut settlements at the outlet and south end and the from agricultural sources. The Taranaki Catchment Commission of the Waitaki Catchment Commission, who examined this issue in 1987, also concluded that though the inflows exceeded outflows, but they did not contribute to the storage due the high sediment contribution vitiating the storage. Consequent to their study of recorded high total phosphorus levels causing the blooms and craeting threats the potential to wildlife and the recreational fisheries, the Commission prescribed interim management guidelines such as: total cessation of aerial top dressing within 500 m of the eastern shore and 800 m of the western shore and around the flow sources in to the lake; restrictions on fertilizer use for agriculture; access to streams for spawning activities and to eatsblish a "deer fence" on the northern end of the wetland; stop all activities related to cultivation on the shores of the lake; stop building of the hut settlements around the lake; install individual of household effluent storage or septic tanks; diversion of sewage outside the catchment. These measures were implemented by the the Mackenzie District Council under a District Plan 1997, under the title "Lake Side Protection Area around Lake Alexandrina". Progressively implemented since 1985, the redeeming feature of these actions is that the heavy algal blooms of the 1980s are now infrequent and limited to frequency of once in three years.

Ecology
There is plenty of wild life in the lake catchment. 45 species of birds which include the southern crested grebe, shoveler and scaup have been reported. Australian Shoveller is a common bird seen in the lake area. Pelicans, black swans and ducks are a common sight in the lake area. Paradise shell ducks flock to this lake in the south island during the summer season. They seek sanctuary here when they become flightless during their moult.

Vegetation
Spread of Elodea Canadensis species has been arrested in the lake and this is attributed to the steep slopes on the east and west sides of the lake and turbulence caused by high winds of 10-14m/sec.

Aqua fauna
The lake has good stock of fishes of which the brown, rainbow trouts and salmons are well known to fishing enthusiasts. The trouts are not found in abundance because of inadequate space for spawning, though the lake has trout food. However, these two species do grow into a large size and each weighing as much as 2.5 kg on an average. Some of prize catch could be of 4.5 kg weight of rainbows and 6.3 kg of brown variety trout (which generally are found along the shores of the lake) where flies and insects abound.