The sampling sites cover a range of land uses and catchment land cover. Monitoring is focused on areas where there is potential for some pressure on water quality due to urban or farming activity. Therefore, many low- risk less populated river catchments are not monitored regularly.
The quality of water in much of Otago is among the highest in New Zealand. Over the past 10 years, water quality monitoring has shown that the rivers draining the higher altitude and lesser developed areas, and the outlets of the large lakes in Central Otago, consistently have excellent water quality. Rivers with very good water quality also include the Kawarau, Cardrona, Catlins, Shag, Waikouaiti and Waipori.
The effects of urbanisation and intensive farming are putting pressure on water quality and aquatic ecosystems. Dunedin’s urban waterways have some stormwater contamination and intensive farming is having a detrimental affect on rivers in south and west Otago. However, water quality is improving in those areas which did have problems caused by larger urban and industrial waste discharges (point source pollution).
The distinctive and characteristic landscape of Otago includes the Southern Alps and alpine lakes, large High Country stations, dry central areas with tussock grassland and tors. There are dramatic coastlines around the Otago Peninsula and the Catlins and lowland pasture country is common in the west.
Approximately 23% of New Zealand’s lake surface area occurs in Otago and the region produces 17% of New Zealand’s hydroelectric generation. Despite large total water volumes present in the region, many areas of Otago are locally short of summertime water and irrigation is an important feature.
Rainfall throughout Otago is highly variable. Predominant westerly winds and strong mountainous influences caused by the Southern Alps result in the Clutha headwaters receiving up to 2,400 mm as an annual average. Central Otago receives much less rain lower due to the rain shadow effect of the Alps, with Alexandra and the Upper Taieri receiving on average less than 400 mm annually, the lowest totals in Otago.
The Manuherikia Valley has an average of between 400 and 500 mm and the Shag and Kakanui an average of 600 mm. Strong southerly, south-easterly or easterly winds can also being heavy rain to the south and east of Otago. Average annual rainfall in the lower Clutha catchment is about 600 mm, the Pomahaka catchment 850 mm, and the upper Water of Leith more than 1,000 mm.