Garth Eyles: Lake Tutira - the real facts!

Garth Eyles

Recently, Lake Tutira has received bad press.

We are left with the impression that nothing has or is being done.

Nothing could be more incorrect as a huge amount of work has been done, and will be done in the future.

The lake is a Wildlife Refuge administered by the Department of Conservation. The immediate surrounds are a Recreational Reserve also administered by DoC.

The remainder of the immediate lake catchment is owned by various individuals or organisations; the largest owner being Hawke's Bay Regional Council, which owns 462ha on the eastern side, known as Tutira Country Park.

The lake is one of three formed by landslides which dropped off the adjacent cliff into the valley. The stream backed up until it found a natural outlet which was within 200m of the natural inlet at the northern end resulting in the lake being almost a closed system.

So, 7000 years of sediment and organic matter have been deposited in the lake instead of being carried down-stream.

Herbert Guthrie-Smith, in the 1870s, converted the natural fern cover to English grasses and a massive amount of erosion followed.

This removed most of the soil on the steep slopes, depositing it in the valley and lake floors. Cyclone Bola, in 1988, was the most recent event, depositing an estimated 773,000 m3 of sediment in the lake.

The lake is typical of those in summer dry hill country as most suffer from regular algal blooms. The only difference is that this lake has high recreational values.

Water quality is not a new problem despite what some people say. By 1974 it was so bad that a Lake Tutira technical committee was established to study the problem. They identified phosphorus inputs needed to be reduced by a factor of five to nine times. The committee recommended:

• Sandy Creek, at the northern end, be diverted as it was the main source of phosphate pollution. The diversion was completed early in the 1980s, destroyed by Cyclone Bola and replaced. There has been no maintenance since 2012.

• The margins of the lake were to become a reserve, fenced and planted with natives.

• A large proportion of the wider catchment needed to be forested and management practices improved. A catchment control scheme was developed and implemented in 1980. It was not completed due to the agriculture economy collapsing.

• To deal with the existing algal problem an air pump was placed in the bottom of the lake and used to aerate the water for two years. The Department of Agriculture identified that this was effective but was too expensive so the programme was discontinued.

It was not until 1998, when the Hawke's Bay Regional Council bought 462ha on the eastern side of the lake to create Tutira Country Park that significant work resumed. The council had the choice of planting the whole property in an erosion control forest or creating a combined recreational park and conservation reserve.

It chose the latter option. A camping ground was developed and exotic trees space planted for erosion control. Areas further from public view were forested to maximise protection.

Blocks of natives were planted at the valley mouths to hold up sediment in future storm events. More recently, all the steep slopes have been planted in manuka. Walking tracks of varying difficulty allow the public to take advantage of the fabulous views across the lake.

In 2008, Biosecurity NZ introduced grass carp into the lake to remove Hydrilla, one of the worst submerged aquatic weeds in the world. Soon after, a buoy was located in the lake to gather detailed water quality information from the surface to the lake floor.

On the western side, the Guthrie Smith Trust continues to develop an arboretum and to minimise runoff and nutrient movement into the lake.

I understand that, currently, there is a major new effort to see if management practices over the whole catchment can be modified to minimise nutrient and sediment run-off, and to apply new measures which could significantly reduce the nutrient loading in the lake and, therefore, the frequency and degree of algal blooms.

So yes, there is still a major problem within the lake. I understand the council is working with the community to reduce the in-lake nutrient levels. But this will be a long-term task involving the whole catchment.

I do not believe it is practical to expect the water quality to change overnight. It may take many years to create the mythical crystal-clear waters people seem to remember.

Garth Eyles is the author of A Short History of Tutira Country Park and was involved in the development of Tutira Country Park from its inception in 1998 until 2008.