On December 4 the Otago Regional Quality received scientific papers on the state of our deep alpine lakes.
By one measure they reported that the water quality in Lakes Wakatipu and Wānaka was good. That was the most disturbing news I’d had all year.
Why? Because the last time they were assessed, they were classed as excellent.
The reports have provisos that some of the changes are not statistically significant, but they also say that for both Wakatipu and Wānaka, the changes in submerged vegetation suggest a reduction in water clarity over time. There are increasing chlorophyll a concentrations in the lakes since 2017. The presence of lake snow is a concern as well.
Measurable changes to big lakes can be decades in the making, and making improvements will take decades as well. That is the same situation as for the nitrate pollution in Canterbury’s aquifers.
The Otago reports also warned that "overseas examples highlight how sensitive large lakes can be to external stressors, such as input of nutrients ... [Once] change starts to occur, it can happen quickly and be very difficult to arrest."
WAI Wānaka raised concerns about the health of the lakes in 2021, and the Parliamentary Commissioner for the Environment wrote to the ORC about it the next year, prompting extra scientific work led by the ORC.
It is easy to throw up our hands in horror at what might be happening to our pristine lakes; easier still to slip it into the too-hard basket. Those reactions aren’t much use though.
In October the ORC was preparing to set a date to notify its new land and water plan. The plan included stronger measures to protect the quality of our urban and rural streams, rivers and lakes. The day before the ORC’s decision the government legislated to prevent it, so that plan is off the table for now.
The plan was part of much wider moves to protect our fresh water. Farmers are planting the sides of streams to act as natural filters for sediment and nutrients that would otherwise run into the water. Urban groups are cleaning up streams and educating their neighbours about stormwater. Other groups are restoring wetlands which again act as giant filters.
There are still significant gaps in knowledge about the deep lakes. The reports identified more monitoring and more research to be done. This will help us better understand the changes and what is causing them. In the meantime we already know that increased urban development and more intensive agriculture spell bad news for water quality.
The health of people and a good quality of life depends on a healthy natural environment. So does a sustainable economy: agriculture won’t thrive in a polluted terrain, and a degraded landscape will not attract visitors.
Along with other Dunedin dwellers, soon I will be heading to Central Otago for some summer recreation. The Rees-Dart Track is calling and we’ll have time with family in Kingston and Wānaka. The lakes are a symbol of why I like to live in Otago.
There’s a well-known saying, "We do not inherit the earth from our ancestors; we borrow it from our children."
We had better make sure that we do everything we can to leave Lakes Wakatipu and Wānaka in the beautiful state we found them in.
• Alan Somerville is an Otago regional councillor.
