The Otago Regional Council (ORC) has this week received a report on river and lake water quality in the region, which acknowledges the quality of water in the “pristine” Upper Lakes Rohe (which encompasses Lakes Hāwea, Wānaka and Wakatipu).

The ‘State and Trends of River and Lake Water Quality in the Otago Region 2000-2020’ report considers freshwater quality at more than 120 across Otago over the past two decades. 

In the Upper Lakes Rohe, the regional council monitors 23 river sites and three lakes.

“The Upper Lakes Rohe encompasses Lake Wakatipu, Lake Wānaka, and Lake Hāwea and all the tributaries that flow into them, effectively acknowledging this is a pristine, high value area,” report author Rachel Ozanne said.

Rachel said the high proportion of glacial rivers, native cover in the upper catchments and the high rain and snowfall volumes play a significant role in the quality of the water in the area.

The report will inform the council’s Land and Water Regional Plan. PHOTO: Wanaka App

“This provides large volumes flowing from pristine catchments of exceptional quality that feeds the Southern Great Lakes,” she said.

Rachel also noted that almost all sites across Otago passed the criteria for ammoniacal-N toxicity and nitrate toxicity and there were obvious spatial patterns associated with the variation in grades - water quality is best at river and stream reaches located at high or mountainous elevations under predominantly native cover. 

“These sites tend to be associated with the upper catchments of larger rivers (e.g. Clutha River/Matau‐Au) and the outlets from large lakes (e.g. Hāwea, Wakatipu and Wānaka),” Rachel said.

Because of the lack of detailed information ORC holds on land use and land management changes at a local or catchment scale the report does not analyse the drivers for water degradation trends.

ORC strategy, policy and science general manager Gwyneth Elsum said the report would inform the council’s Land and Water Regional Plan.

“This report largely reflects the patterns we have seen in the past, which tell us that water quality is best in the headwaters and at higher elevations, but it suffers at sites in smaller, low-elevation streams that drain pastoral or urban catchments,” she said.

As well as informing the new plan, the report would also support ORC and the community to implement other water quality improvement initiatives, Gwyneth said.

The analysis in the report will be repeated next year with data up until June 2022.

The ‘State and Trends of River and Lake Water Quality in the Otago Region 2000-2020’ report can be viewed online here.