But the future of this waterway is murky.
Indeed, the fate of the river now hangs in the balance, as the Otago Regional Council (ORC) grapples with the issues plaguing so many of our waterways, the very same water management challenges faced by other regional councils throughout the country: how to cope with the competing interests of intensive agricultural production and its associated environmental effects, and community aspirations for healthy rivers for recreation and tourism.
The pressures of dramatic land-use intensification in the Pomahaka catchment for several decades have taken a hefty toll on the river, with a marked decline in water quality in the middle and lower reaches.
In response, the ORC, which manages the region's water resources, is planning to set a minimum flow for the river and address the pollution associated with runoff from land within the catchment. This is called non-point source pollution. A minimum flow is an essential component of good environmental management and, if done correctly, will protect the river during summer low flows and help address the non-point source pollution problem.
In support of these processes, Otago Fish and Game Council has developed a detailed position on water quality and quantity standards required to maintain a high-quality trout (and salmon) fishery in the Pomahaka as a step towards more sustainable river management. This paper can be found on Otago's pages of the Fish and Game website.
As well as river-resident brown trout, the Pomahaka provides spawning grounds for a run of sea trout. These behave like migratory salmon and move upstream from their adult habitat in the ocean to spawn in the headwater where eggs are laid in riverbed gravels. And more recently, returning sea-run salmon have also found their way into the Pomahaka to spawn.
Trout, salmon and native fish require clean water for survival and reproduction, but intensified land use in the catchment, first detected back in the late 1980s, has been taking a toll on water quality. Silt from runoff has smothered riverbed gravels, the habitat for aquatic insects on which fish feed. It has also interfered with fish feeding, and nutrient input has increased algal growth. Anglers have noticed a gradual decline in the quality of fishing in the middle and lower reaches, and this has been backed up by research. Although the river seemed to be coming right for a season or two, the next wave of land-use intensification entrenched water-quality declines, and the fishery's popularity with anglers has fallen away.
The ORC is looking to tackle contaminated runoff in the catchment through a proposed rural water quality strategy which includes changes to the water plan and sets new rules for water management.
Details of the strategy are yet to be released, but the initiative deserves to be strongly supported. Fish and Game's only concern is the time required for the new regime to reverse the present situation. With continued land-use intensification, it could easily get worse before it gets better.
Then there is the issue of water quantity. The optimum river flow for freshwater fish is the natural flow, but that is only achievable in national parks. Elsewhere, rivers are a shared resource.
Fish stocks get stressed in high summer when river flows are low and temperatures are high. That can occur naturally in times of drought, but the situation is exacerbated when more and more water is extracted for irrigation.
While prevalent in Central Otago, heavy allocation of water for out-of-stream uses has not been such an issue in South and West Otago. A minimum river flow - at which point surface water-takes for uses such as irrigation cease - protects aquatic life through critical low-flow periods.
For some months now, the ORC has been going through a process of identifying key river values and community aspirations in order to set a minimum flow for the Pomahaka. It initially proposed a minimum flow of 2.5 cubic metres per second (cumecs), but the mean annual low flow is nearly twice that at 4.3cumecs.
Fish and Game believes the suggested minimum is too low, given the community support for a healthy river, the lack of constraints on water availability, the regional importance of the fishery, and taking account of present poor water quality. A minimum flow of 4.3cumecs makes much more sense.
Most local community members (including landholders) with whom Fish and Game has talked value the rural outdoors in terms of recreation values, particularly fishing and hunting. They want productive farms, but they want a productive trout fishery and a healthy river as well.
Fish and Game believes the community can have both the economic benefits of farming, as well as the quality of life that comes from having healthy rivers and productive fisheries by setting reasonable standards for water quality and quantity. The choice is ours.
• Niall Watson is chief executive of the Otago Fish and Game Council.
