December 14 2004

Another beautiful summer by the lake...
but can we still play in the water?

As New Zealanders all over the country flock to beaches and lak
es for the holidays the quality of the water is something we don’t want to worry about. But for holidaymakers heading to the scenic Rotorua lakes recent summers have been disappointing. Last summer’s particularly nasty algal bloom was the worst yet, with health warnings which were more widespread and lasted longer than ever.

Rotorua’s many lakes are the jewel in the region’s crown, and are a great tourist drawcard year-round. Many Kiwi families have spent summers on the lakes, swimming, sailing and fishing in the beautiful surroundings of the area. Unfortunately, some of Rotorua’s glorious lakes aren’t healthy. They are suffering from eutrophication, which in effect means they are becoming ‘soupy’ and suffer seasonal algal blooms.

While that might not sound too severe, the algae blooms have a huge social effect, since the lakes are used extensively by Kiwi families, plus an economic effect on the region’s lifeblood of tourism and trout fishing.

Most lakes in the Rotorua district show some risk of decline. Many are still safe to use all the year, but a few are at risk of continued algal blooms. Lake Rotorua itself last year passed a tragic milestone, becoming ‘super-trophic’, or extremely eutrophic, for the first time.

Some lakes are famous primarily for trout fishing and tramping like the gem of Okataina, some such as Tarawera for fishing and boating and their volcanic history, and others for water skiing and boat racing (Tikitapu or Blue Lake). Rotoiti in particular is a favourite for thousands of boats – fishing, sailing, picnicking, kayaking. While it is the most widely used lake, it is also the one under the greatest immediate threat.

The lakes are all different in size, age and catchment, but the common feature is that they suffer from raised levels of nitrogen and phosphate and the most enriched are vulnerable to cyanobacterial algae. Local government is working with urgency to combat the problems, with support from central government. Community groups such as LakesWater Quality Society, local iwi, and the farming community are actively involved.

But the situation is complicated by the differences between the lakes . Some risk losing oxygen and dying quite quickly, while others are still pristine, but all have some indication of immediate or potential problems. Each needs an individually-designed solution, but all solutions are based on reducing the levels of nitrogen and phosphorus in the water.

While some lakes such as Rotoiti teeter on the brink of being damaged forever, there are some small glimmers of hope from nearby Rotoehu, which over the last two years has shown improvement from its previous seriously degraded state, after efforts to reduce nutrient inputs.

Sadly the algal blooms which affect some of the lakes can be toxic, forcing the Ministry of Health to issue health warnings. Last summer health warnings were more widespread and lasted longer than ever. And every year the warnings are worse.

The situation faced today is largely the result of over 100 years of abuse and neglect from human activities – sewerage, septic tank outflows, soil erosion, intensive farming outflows.

The pollution is mostly due to nitrogen and phosphorus which enriches the lakes and feeds algal growth. It also comes from natural sources like geothermal springs;, and from cold springs rich in phosphorus, such as the beautiful Hamurana Springs.

Can the lakes be saved? There is a good chance they can, if enough is done soon enough. There are two main issues. The first is to immediately reduce the levels of nitrogen and phosphorus compounds going into the lakes. The Rotorua District Council is making a significant investment in sewerage with support from Environment BOP and central government. Sewage schemes are now planned for all lakeside settlements.

The Regional Water and Land Plan will limit nutrient increases in the future,. Environment Bay of Plenty is moving with great urgency to plan emergency measures as well as funding research to close some of the gaps in our knowledge about best way to fix the lakes.

Although farming is contributing to this part of the problem, no-one is seriously suggesting closing down farms and planting pine trees everywhere or letting the land revert to blackberry and gorse – that wouldn’t save the lakes and the economic costs would be huge. A solution to the nitrogen outflows from farms is more likely to come in the form of significant technological advances to reduce them.

These are to be tested in the field, hopefully next year, with the help of the Sustainable Farming Fund. Groups working to rescue the lakes are also receiving significant assistance from the Sustainable Management Fund. However there are still more than 100 years of pollutants already in the underground water system that will have to flow through to the lakes. And the sediments at the bottom of the lakes have a big store of nitrogen and phosphorus as well.

There are a number of options for dealing with these ‘historical’ elements nearly ready for decision. Some involve safely channelling the nutrient inflows away from some lakes and stopping them feeding the algae. Incidentally these would improve the Kaituna River as well, by reducing the obnoxious algae flowing downstream. Others include precipitating them using activated clay or other compounds.

This is gradually starting to happen and the first trial was done this year on Lake Okaro. The problem isn’t unique to the Rotorua region, but these lakes are at the sharp end of the threats faced by many New Zealand lakes.

The difference is that here the damage is happening today and is not just a distant worry. Prospects for this summer hold little good news. There has not been a reduction in nutrient inflows yet - so we can’t yet expect improvement – in fact some inflows are still increasing. And until the lakes themselves see the plans put into action, blooms can be expected each year in the worst lakes – with some variation in severity because of climatic influences. But the diversity of the Rotorua lakes makes them a great playground still.

Whatever the summer brings there are limpid lakes great for swimming, large trout to be caught, lakes safe for sailing, kayaking and skiing. These lakes are still stunningly beautiful. They are for all New Zealanders to enjoy and for international visitors to envy – it’s worth a great deal to New Zealand to keep them that way.

ENDS

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