2. LAKE OKATAINA

Lake Okataina is a beautiful clean lake surrounded by bush. Its full name is Te Moana-i-Kataina-e-Te Rangitakaroro - the sea where Rangitakaroro laughed. Rangitakaroro and his warriors were sitting by the lake when one of his men called it the sea. This was seen as a great joke and Greg Tuuta laughter echoed around the lake. In pre-European times, Lake Okataina was part of a route from Lake Tarawera to Lake Rotoiti. Canoes were used on the lakes then carried across the land between each lake.

Okataina is an ‘oligotrophic’ lake - very clean and clear with little nutrient and little sediment in it. Surrounding bush intercepts and takes up runoff from various farming blocks in the catchment, reducing the movement of nutrients and silt into the lake. The bush also provides shade along the shoreline and tributaries which helps keep water temperatures down. The lakes maximum depth is 78.5 metres and it covers an area of 10.83km 2.

2.1 HOW TO GET THERE

The lake is situated about 30 kilometres from Rotorua, off State Highway 30. The turn off is at Ruato Bay of Lake Rotoiti and there is 7 kilometres of winding road to reach the lake. The lake is about 2 kilometres beyond the Okataina Outdoor Education Centre. The bush is teeming with birds and there are many grades of walk available.

At the end of the road, on the lake edge there is a grassed picnic area with some shade trees and a shelter. Public toilets can be found near the picnic area. No rubbish bins are provided in a bid to discourage possums, rats and wasps.

In late summer and autumn, wasps can be prevalent. As a precaution at this time of year, take antihistamine cream, check that people allergic to wasps have medication with them..

There is an excellent interpretation board at the picnic area, telling of the history and formation of Lake Okataina. The lake is volcanically formed and has a complex geological history.

2.2 VOLCANIC BEGINNINGS The Okataina Volcanic Complex has shaped the history of the Rotorua basin with large ignimbrite eruptions and subsequent collapses into the emptied magma chamber creating a caldera. There have also been rhyolitic eruptions producing the dome complexes of Tarawera and Haroharo.

Lake Okataina was once an arm of Lake Tarawera until a rhyolitic lava flow emerged between the two 7000 years ago. This has left Lake Okataina with no outlet apart from the fissured lava at the Tarawera end Bay of Plenty Super Sites: 9 Lake Okataina –Super Site Resource 3

of the lake. As a consequence, the lake levels vary hugely with rainfall and have been known to rise by as much as 10 metres. For more information look up: http://www.gns.cri.nz/earthact/volcanoes/nzvolcanoes/okatbookprint. htm

2.3 NGATI TARAWHAI

Ngati Tarawhai are the principle iwi of Okataina with their main pa on the Te Koutu Pennisula. The area is steeped with fascinating cultural history. (Much of this is detailed in the corresponding education resource ‘Lake Okataina Scenic Reserve’ and you are encouraged to use these two booklets together). Fluctuating lake levels were the main reasons for Ngati Tarawhai moving away from the area before 1900. In 1921 Ngati Tarawhai gifted the shores of Lake Okataina to the crown to be set aside as a reserve. As a condition of this endowment, the reserve is now administered by the Lake Okataina Scenic Reserve Board which comprises of members of Ngati Tarawhai.

2.4 LAKES After a period of stabilising, volcanically formed lakes begin as clean, deep lakes with low sediment and low nutrient concentration - (oligotrophic ) and slowly change to become less clear (turbid) with higher amounts of sediment and nutrient through a process called eutrophication. Eutrophication is a natural process often sped up by human activity in the surrounding catchment such as the disturbance of soil and vegetation and the addition of fertilisers and animal wastes. These activities influence the quantity and type of sediment and nutrients reaching the lake. Discharges into the lake via waterways also feature as a source of nutrients. Too much nutrients, especially nitrogen and phosphorus can further the growth of undesirable aquatic plants and cause problematic ‘algal blooms’.

More than 25 metres deep.

Clarity excellent.

Little sediment.

Lots of oxygen available at all depths.

Oligotrophic Lake (Generalised)

Less than 15 metres deep.

Clarity poor.

Lots of sediment.

Tends to stratify in summer, leaving little oxygen for bottom -dwelling fish.

Eutrophic Lake (Generalised)

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2.5 WATER QUALITY

Dissolved Oxygen Dissolved oxygen is the oxygen dissolved in water and is necessary for the respiration of fish, molluscs, crustaceans, invertebrates (bugs), bacteria and plants (at night time). Oxygen gets into water either by slow diffusion from the surrounding air, turbulence caused by wind aerating the water, or as a by-product of photosynthesis.

Oxygen is mixed through the lake by wind turbulence. Mixing also occurs through daily heating and cooling of the lake causing the denser night-cooled surface water to drop to the bottom of the lake. This bottom water is displaced and moves to the surface. During summer and autumn, lakes can become separated into layers of different densities. Due to the behaviour of water at different temperatures, light water remains as the top layer, with the dense water positioned in the middle (the thermocline). This layering is called stratification and the dense mid- layer of water limits mixing and results in the bottom layer of water becoming deoxygenated during late summer and early autumn through respiration of bacteria.

Stratification occurs mostly in eutrophic lakes like Lake Rotorua. Fish cannot tolerate this - trout for instance take advantage of more oxygenated water at stream mouths and shore springs at this time. Heating of water and pollution by organic matter such as sewage reduces the amount of dissolved oxygen in the water.

Temperature Water temperature is related to weather and is affected by human activities such as discharges of heated water into waterways and cutting down vegetation which shades the water. Water temperature determines what aquatic life can live in the lake. Different organisms have different tolerances - a trout’s optimal temperature range is 13 - 15°C but pest fish like catfish tolerate warmer temperatures and lower dissolved oxygen levels than trout.

Clarity/Turbidity Clarity is how far you can see through the water and this depends on the turbidity or cloudiness of the water. Turbidity is caused by material such as silt, algae and organic material that is suspended in the water. It is increased when there is disturbance of soil and removal of vegetation in the catchment. Silt is brought down streams and rivers, particularly during rainfall events and transported into lakes and estuaries. Silt can travel over surprisingly long distances. Other causes of turbidity include the growth of phytoplankton and the decay of algae which occurs in late autumn after an ‘algal bloom’. If water clarity is poor it blocks the sun from reaching to the aquatic plants reducing photosynthesis and thereby the amount of dissolved oxygen in the water. Many organisms including fish need this oxygen. Aquatic plants are also an important source of food. Turbidity affects respiration of fish, molluscs, crustaceans and invertebrates clogging up their gills.

Nitrate Nitrate is the form of nitrogen available as a nutrient to plants. It enters lakes through the breakdown of vegetation, run-off from fertilisers and

Bay of Plenty Super Sites: 11 Lake Okataina –Super Site Resource 3

animal waste, sewage and fixation by cyanobacteria (blue-green algae). Excessive nitrates can lead to algal bloom.

pH pH is the measure of how acid or alkaline the water is. The pH scale goes from 1 being very acidic to 14 which is very alkaline. pH is affected by surrounding rock type, runoff, sewage and nutrient levels. High nutrient levels cause growth of algae and plants and this in turn raises the pH value. Animals and plants are affected by changes in water pH and have different ranges of tolerance. The safe range for an aquatic habitat is around neutral - pH range 6.5 - 8.5.

Phosphorus Inorganic phosphate is the form of phosphorus available as a nutrient to plants. It is necessary for all forms of life but occurs naturally in low concentrations. Phosphorus enters lakes through weathering of certain rocks (apatite and guano), runoff from fertiliser, sewage, detergents and the breakdown of organic matter. Inorganic phosphate is locked up in sediments and only released when the bottom of the lake becomes anoxic (without oxygen) when a lake stratifies. Once the stratification layers break down the inorganic phosphate is mixed through the lake and can cause algal blooms and excessive weed growth.

All of the factors described are inter-related: - abundant plant growth and algal blooms increase pH and turbidity, increased temperature reduces dissolved oxygen and so on. Look at http://mfe.katipo.co.nz/freshwater/lakes/index-rotorua.html to compare the water quality of the Rotorua Lakes. These two websites also help with understanding water quality: - http://www.k12science.org/curriculum/bucketproj/resources.html http://www.watere.org.nz

2.6 FISH Lake Okataina supports the native common smelt, common bully, banded kokopu and koaro. These species are normally diadromous (migratory) and therefore require access to the sea to complete their life history. However, in the Rotorua Lakes the populations have become landlocked with no access to the sea. About half of New Zealand’s 35 native freshwater fish, are diadromous (migratory). Introduced species to Lake Okataina include rainbow trout, gambusia and goldfish. The common smelt was introduced to the lake in the early 19 th century. There are also koura (small freshwater crayfish) and freshwater mussels in the lake.

Threats to native fish include predation and competition for resources by the trout, gambusia and goldfish; modification of habitats such as removal of trees which provide shade and cooler temperatures; sediments which reduce water clarity; loss of habitat and obstructions like dams and culverts to normal migration. In Lake Okataina, vegetation around the lake is intact and the water clarity excellent, however the native fish suffer from the predation and competition by the introduced fish.

Bay of Plenty Super Sites: 12 Lake Okataina –Super Site Resource 3

Common Smelt

The common smelt was introduced into Okataina in the 1930s, coming originally from the lower reaches of Waikato River. Their food consists of adult and larval insec ts and large zooplankton crustacea. Smelt are a small (about 90mm) silvery fish and only live for around 2 years. They are an important source of food for trout.

Common Bully The Common Bully is a bottom dwelling fish with a reduced swimbladder which allows it to sink. They feed on small bottom- dwelling insects and crustacean. Due to their versatility they have not suffered from gross reduction in numbers as many other native fish have. They can live for over 3 years and grow to approximately 110mm in length. They ca n be seen feeding off the bottom of the lake bed near

shore.

Banded Kökopu The banded kökopu is a scaleless and nocturnal fish living within small streams where there is overhanging vegetation. Their food consists of insects and spiders which have fallen ont o the water’s surface from overhanging vegetation. They can grow to around 280 mm long, with fish living to more than 10 years old. The young are excellent climbers – useful for migration upstream. They spawn during floods in the leaf litter along the str eam margins. The eggs incubate until the next flood which stimulates hatching of larvae.

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Koaro

Kim Young

The koaro is usually a long, thin tubular fish, covered with golden blotches and bands. However, in landlocked populations it appears more rotund and has no distinct golden patterning. Adults are abundant in the lake during summer and shoals of juveniles can be found around lake margins during late summer and autumn. Prior to the introduction of trout it is thought that the koaro were abundant, and provided a food source for the Ngati Tarawhai people living there. Downwards facing pectoral fins aid young koaro to be remarkable climbers – useful for migration up bouldered streams and dams. Koaro grow to about 170mm long. To date the oldest koaro found is 8 years but it is considered that they live longer than this.

Two excellent sites for finding out more about New Zealand Freshwater Fish are: - http://www.nzfreshwater.f2s.com . http://www.niwa.cri.nz/NIWA_research/fwfish atlas/

2.7 AQUATIC PLANTS There are also native aquatic plants in Lake Okataina but these are being overgrown by the Lagarosiphon major and Elodea canadiensus (introduced oxygen weeds). If you walk to the end of the jetty you can see the native Myriophyllum sp.being outcompeted by Lagarosiphon which makes a dense and fast growing mat taking up most of the available light and space. Find out more on: http://www.niwa.cri.nz/pgsf/AquaticPlants/species.html (Photos by J. Clayton)

Myriophyllum sp. Myriophyllum sp. are native submerged aquatic plants that are found throughout New Zealand in lakes and streams. Plants grow to 3 metres tall in water up to 3.5 metres deep.

They flower from November to March, and the flower heads protrude just above the surface of water. They reproduce by seed, from fragments and rhizomes.

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Lagarosiphon Lagarosiphon is a submerged aquatic plant that has been introduced to New Zealand through the use of it in aquariums. It grows in shallow water and to depths of up to 6.5 metres. It forms dense stands and reproduces and spreads within the water and between lakes and rivers from stem fragments. These fragments can be transported on boats and boat trailers. Lagarosiphon plants soon overgrow most other vegetation in clear waters. The spread of this and other prolific lake weeds is the reason why boats and their trailers should be washed down after use.

2.8 THE FOOD CHAIN Although there are a good variety of waterbirds at Lake Okataina, the numbers are small when compared with those of Lake Rotorua. This is most likely due to the low concentration of nutrients in the lake.

Nutrients such as nitrogen and phosphorus encourage the growth of aquatic plants and phytoplankton (photosynthesising plankton). Zooplankton eats the phytoplankton. Small crustaceans, bugs, shellfish and small fish eat zooplankton and phytoplankton. Big fish eat small fish. Different birds eat different things. Some birds eat small fish eg. the white-faced heron, some eat bugs and shellfish, some eat dead material and there are birds that are wholly vegetarian like the black swan.

A small quantity of nutrient in the lake means that fewer organisms can be supported altogether but the most obvious thing to the casual observer is the shortage of water birds. Bush birds around Lake Okataina are prolific in comparison because they have a productive food source.

The yellow arrows in the following diagram indicate the flow of nutrients in a lake.

Inflow of nutrients via streams and rivers

Phytoplankton Zooplankton

Death, decay, and waste from all organisms

Molluscs, worms, crustaceans Sediments

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