The treatment of waterborne wastes can be broadly divided into two stages, viz., primary treatment and secondary treatment. In addition, a third stage or tertiary treatment process may be required in some circumstances to protect the uses made of the receiving waters. Primary treatment is concerned with the separation of as much as possible of the solids carried in suspension in the sewage, and their subsequent treatment and disposal. Solid matter is removed in preliminary treatment units, such as screens and grit traps, and by settlement in tanks which provide quiescent conditions for the removal of the solids by gravity settling. Secondary treatment involves the biological stabilisation of the liquid effluent, including the remaining suspended solids and the dissolved solids, from the primary treatment processes. Examples of secondary treatment are the trickling filter and activated sludge processes. The tertiary treatment or “polishing” of an effluent to remove any residual polluting matter or bacteriological contamination may be effected by the use of sand filtration or oxidation ponds, among other processes. In some cases two or more of these stages of treatment are carried out in a single treatment unit such as an oxidation pond or a Pasveer oxidation channel.

In 1961 Government approved the payment of subsidies to local authorities towards the cost of providing sewage treatment and disposal facilities for towns with populations of less than 20,000. Because the cost per head of population served by such facilities is generally higher in the case of small communities than for cities, the subsidies are available on a graduated scale, the highest subsidy (50 per cent) being payable to communities with a population of less than 1,000.

Under the Waters Pollution Act of 1953, the Pollution Advisory Council was established with the responsibility of preventing and abating water pollution throughout New Zealand. In 1963 regulations were made under this Act to permit the Council to classify inland and coastal waters according to their established or potential uses. These classifications and water uses are defined as follows:

Water quality standards have been laid down to protect these different uses in the receiving waters. Following the classification of any waters, all outfalls discharging polluting wastes into them must be registered and covered by a permit setting out the conditions under which discharge may be made. The permit also indicates the standard of treatment of the waste discharge which the Council considers necessary to maintain the prescribed standard in the receiving waters. It then becomes an offence to allow the discharge of a waste which is likely to cause the quality of the receiving water to vary outside this standard.

How best to deal with several million gallons a day of contaminated wastes is a huge and costly problem. A survey conducted in 1962–63 by the Ministry of Works indicated that about 85 per cent of the total population of the cities and boroughs (1,639,000) was served by a public waterborne system of sewage disposal. The proportion of this urban population provided with a generally satisfactory form of public-sewage disposal system was just less than 60 per cent, while a further 15 per cent was served by an unsatisfactory system.

For every million gallons of water used in the home and by industry, nearly a million gallons of contaminated water have to be disposed of into inland or tidal waters. In the early days of the settlement of New Zealand, pollution of natural waters did not present a great problem. The population was small and as there were few waterborne-sewage disposal systems, the bulk of the human wastes did not reach inland or tidal waters. As time went on the population increased considerably, urban communities grew into large towns, farming became more intensive, and secondary industries developed. This led to the introduction of waterborne-sewage disposal systems with outfalls into streams, rivers, harbours, or ocean waters, and to outfalls from industries discharging large quantities of liquid wastes, particularly those associated with primary industry, such as freezing works, dairy factories, woollen mills, and such like. The consequence was that more and more of the country's natural waters were polluted in varying degrees, and it became more difficult, for example, to locate uncontaminated sources for urban and industrial water supplies.

With the growth of the population, development has spread into areas which were formerly remote places. Whereas years ago discharges of polluting wastes from the more remote towns and rural industries did not cause offence to many, the increased use of the motor vehicle and improved roading has meant that areas which were once regarded as out of reach are now popular recreational areas where the quality of the water is of considerable concern to the public.

Water-boatman (Arctocorisa arguta) and Back-Swimmer (Anisops wakefieldi).

Both these insects have many things in common. They are true bugs; they live in still, freshwater areas especially ponds and stagnant pools throughout New Zealand; and their means of locomotion in water is by the rowing-like action of their hind pair of legs. The back-swimmer swims only on its back while the water-boatman propels itself dorsal side uppermost. Both are carnivorous and feed on insect and other animal life in the water. Mosquito larvae are an important part of their diet. The water-boatman can be distinguished by its body which is compressed dorso-ventrally while the back-swimmer has a body laterally compressed. Both insects are about ½ in. in length.

by Roy Alexander Harrison, D.SC., Senior Lecturer in Agricultural Zoology, Lincoln Agricultural College.

As in most other countries, water ski-ing in New Zealand is a new sport. Although it originated in Europe and the United States during the late twenties, it is only in the last few years that the pastime has become popular here. The first clubs were formed in 1954 and 1955 at Auckland – the Auckland Water Ski Club and the New Zealand Water Ski Club. These were quickly followed by others. Soon, however, the rapidly increasing popularity of the sport was bringing unlooked-for problems – unskilled boat drivers and skiers causing accidents and near accidents. The clubs, still in their infancy, did their best to overcome these problems. During 1956 and 1957 the Marine Department received so many complaints about irresponsible boat drivers and water skiers that the banning of the sport was considered. Those associated with the sport since its beginnings agreed that some firm action was needed to place it on a sound basis, and in 1959 the Auckland clubs made a move towards the formation of a national organisation. There was close liaison with the Marine Department and harbour boards and an offer of cooperation was made and accepted. A meeting at Wairakei in September 1959 inaugurated the New Zealand Water Ski Association. Immediately after its formation, the association made a recommendation to the Marine Department and to harbour boards that ski lanes be provided wherever ski-ing was popular and wherever there was enough room on the beaches. The Department drew up regulations governing the sport in areas under its control and these were also adopted by the harbour boards.

With the club movement continuing to grow, interest turned towards competitive ski-ing; the rules adopted in the United States were, and still are, the basis for competitions in New Zealand.

During the Christmas period 1959–60 the first national championships were held at Picton, sponsored by the Marlborough Cruising Club. The first annual meeting was also held and those officials elected at the inaugural meeting were re-elected. From this time on, the association, with headquarters at Auckland, went from strength to strength. Hitherto unknown clubs from all over the country applied for affiliation and helped in the organisation and administration of the sport. During 1960 the regional associations performed their true functions of drawing together all clubs in their area for the purpose of holding local tournaments. These culminated in the second national championships held in Auckland over Easter 1961. In the space of one year the standard had improved enormously and, in the final events, several competitors were well up to world standard.

Since 1963 two new divisions have been included in the National Championships. These are Senior Men's Overall Champion, and Senior Women's Overall Champion.

According to the record book, water polo has been played in New Zealand since 1892, 23 years after the game evolved in England. Christchurch was the host city to the first championship meeting which was held in that year. At first the sport was confined to the main cities but, as the smaller centres built pools, so the game spread. Today, towns like Hamilton, Te Awamutu, Wanganui, Napier, and Hastings have teams, while Lower Hutt has emerged as a centre strong enough to hold its own with any of the main cities. Until 1909 water polo was played only on an interclub basis. Since then provincial teams have held frequent competitions, with Canterbury dominant till the early thirties and Otago strongest from then till the late forties. The South Island's prominence then declined and national supremacy moved north, fluctuating between Auckland, Wellington, and the Waikato.

Water polo is administered by the New Zealand Water Polo Board under the rules of the New Zealand Amateur Swimming Association. Though the sport has been played since before 1900, it did not have its own administration until 1951. Before this it was administered by the secretary of the association. The Board's chairman, secretary, and three members are elected each year by delegates from the various local water polo boards which control their own competitions and send teams to the national championships. The championships decide which province will hold the national trophy, and they alternate between those main centres which have adequate facilities. As well, an interclub championship is held for the Ryan Cup.

Water polo has been played in trying conditions, more so in its earlier days than in more recent times. A game at Wellington in 1911 is still remembered. It was played in water of 56° and lasted 50 minutes, causing the collapse of several players and the admission to hospital of a goalkeeper. In New Zealand, water polo is a man's game. For a short while, and following the example of some overseas countries, women's water polo was tried on a modest scale. But the attempt was soon abandoned.

Of all the exponents of the sport in New Zealand, Lord Freyberg, was probably the best known. A very keen player about 1910, he was active in training an Auckland team.

In 1960, after many years of sometimes heartbreaking effort, New Zealand water polo finally took part in Olympic competition when it met Australia at Melbourne in an elimination game, losing 7-1.

Other international matches played are as follows:

• 1950 Empire Games at Auckland:

• New Zealand 4, Australia 1

• Australia 13, New Zealand 2

• Australia 5, New Zealand 2

• 1951 Canterbury Centennial Games:

• Canterbury 10, New South Wales 5

• Australia 7, Canterbury 4

• Australia 6, Canterbury 4

• Australia 6, New Zealand Universities 1

In addition, there are some introduced plants which have become very abundant, in some cases blocking streams and rivers. Among these is watercress, Nasturtium officinale, one of the plants introduced by early colonists as a food, which became a nuisance in the Avon River and streams about Christchurch. Pond weeds, which have become very abundant and in certain instances a serious problem of control, are Ottelia ovalifolia, from Australia, and Aponogeton distachyon, a water hyacinth from South Africa. A greater threat comes from another water hyacinth, Eichhornia crassipes, the growing of which is strictly prohibited in New Zealand. It has attractive pink-mauve flowers with yellow and purple markings on one petal. It grows very rapidly, has extensive rhizomes, and may root in mud or float on water.

by Olive Rita Croker, M.A., Botanist, Wellington.

Two other small plants growing in muddy places and often submerged are Mimulus repens and Limosella tenuifolia (mudwort), relatives of the monkeymusk (Mimulus guttatis). Some species of buttercup of similar habitat are Ranunculus rivularis (poisonous to stock), R. fluitans, and R. macropus. Also growing in wet mud, completely submerged at times, are Callitriche verna, the light green starwort; Elatine gratioloides, which creeps under water at edges of lakes; Ludwigia palustris, water purslane, with a mat-like form of reddish colour; and Tillaea sinclairii, found mainly in the South Island. These are all tiny plants. More conspicuous are sedges and rushes. Of many species of Carex a few grow near the edges of water. The genus Scirpus includes species from 3–10 ft high of which the best known are S. lacustris, our tallest sedge, common throughout the country; S. perviridis, usually 5–6 ft, of the North Island, and the shorter S. caldwellii, found in both Islands. Species of Eleocharis and of Cladium are other familiar sedges. The raupo, Typha muellerii, known to the Maoris as koreire, is probably the best known of our plants of watery swamps. Before there was any systematic drainage of the country, extensive areas were covered by raupo. The tall flower stalks have dense masses of tiny flowers, male flowers above and female flowers on the lower part. This plant was useful to the Maoris in various ways: the rhizomes for food, the flower heads and hairy fruits for plugging holes in canoes, and pollen mixed with water baked as cakes. Early settlers used inflorescences for stuffing pillows and beds and the leaves for thatching roofs.

A very interesting plant which may cover a pond so closely that it appears as a grassy patch is the tiny fern Azolla rubra which floats on the surface of the water, the arrangement of overlapping leaves enabling it to remain buoyant. Each leaf consists of two differently shaped lobes, the upper one being above the water so that a cavity is formed between the two lobes in which a tiny freshwater alga finds a home. This is Anaebena, a member of the Nostoc family. Isoetes alpinus is a lycopod with stiff green leaves, found in Lake Taupo, and in lakes on the mountains of the South Island.

Of the flowering plants we may consider a few. There are no trees or shrubs of fresh water comparable to the mangroves of salty estuaries, but many monocotyledonous plants live on the edges of lakes, rivers, or in wet swamps, and some appear to live floating on the water. Long underground stems are common, and sometimes there is a thick rhizome in which food is stored for the season when leaves are shed. On the surface of slow-moving streams and ponds in most parts of New Zealand may be seen the floating, oval leaves of species of Potamogeton. P. cheesemanii is the commonest, while P. ochreatus and P. pectinatus are abundant also. The latter lives completely submerged; even its flowers and fruit are under water. In other types there are long coiled stems by which the flowers come to the surface where pollination takes place. This happens in Ruppia spiralis, where after pollination the stalk recoils and the fruit ripens at the bottom of the water. There the long stalk on each fruit becomes tangled with others so that large rounded masses of fruits are formed. This plant is very common in Lake Ellesmere.

Among floating plants are the tiny duckweeds, which form bright green masses on the surface of still water, with small hanging roots. Lemna minor is a bright green plant of wide distribution; Spirodela oligorrhiza, slightly larger is found only in parts of the North Island; Wolffia arrhiza, found mainly near Wellington and in Canterbury, is also bright green, and disappears to the bottom during the winter. The water milfoils have tiny, much divided leaves, especially those completely submerged. There are four species of Microphyllum commonly found in New Zealand.

There are three species of bladderworts (Utricularia) described as found in New Zealand, but U. mairii, which grew in Lake Rotomahana, has not been seen since the Tarawera eruption of 1886. This was a floating plant similar to U. protrusa with finely divided leaves. The bladderworts are curious plants with finely divided leaves and bladders in which insects become trapped and, as they disintegrate, form part of the food of the plants. A third species has roots: this is U. novae zealandiae found in the North Island as well as in Canterbury on wet peat subject to frequent flooding.

The algae are that group of simple plants forming with the fungi the class Thallophyta. Algae contain chlorophyll and obtain oxygen and carbon dioxide from the water in which they live, thus enabling them to carry out the normal functions of green plants though, in seaweeds, this colour is often masked by other pigments, brown or red. There are two main groups of algae, the freshwater and the marine forms. The marine algae or seaweeds are dealt with in a separate article. Though a great deal has been published about the seaweeds found round our coasts, there has been very little published about the large group of freshwater algae, though at intervals there have appeared lists of the names of species found in different localities, showing that a few hundred species are present in our waters.

The freshwater algae are a group of very interesting plants. It is only when these forms are found in large numbers as, for example, as pond scums, that they are visible to the naked eye. Small areas of standing water may appear reddish in colour because of multitudes of Haematococcus, one of the few forms with any pigment other than chlorophyll. But with the aid of a microscope a drop of water from pond or stream is found to contain many varied and fascinating forms of tiny plants. These are of considerable importance for they manufacture food and so form the first stage in the provision of food for animals. Freshwater algae live under varying conditions and are of many forms. They are found in slow-moving rivers and streams, in lakes and ponds, in ditches and stagnant pools, and on damp earth. They are of varied form. Many are completely unicellular, some appear as filaments which form pond scums, while others appear as hollow spheres or in more complicated forms. Their methods of reproduction may be by simple division, or by some elaborate methods of sexual reproduction. Of the free unicellular forms are Diatoms (of many intricate designs), Desmids (often crescent shaped), Haematococcus and Chlamy-domondas (moving quickly with two cilia). Among the pond scums are many forms which appear as long fine green hairs, slimy to the touch, common among these are Spirogyra, Zygnema, Vaucheria, and Oedogonium (with complicated methods of reproduction). The Stoneworts (Chara and Nitella) form long brittle colonies on the beds of rivers and lakes. The hollow spheres of Volvox, whirling through the water, are formed of tiny similar plants, but with complicated methods of reproduction.

Many other freshwater algae might be mentioned as Sphaerella, Cladophora, Ulothrix, Oscillaria, and the tiny Protococcus and Pleurococcus on damp earth and tree trunks, but, though they seem to be common in most places, there is little exact information concerning their distribution in New Zealand. In the thermal regions there are some members of the Cyanophyceae (the Blue-Green Algae) which are noteworthy for the fact that they grow in water of high temperature and on damp clay which is very hot.

Many mosses and liverworts live more or less in water. These groups of plants are dealt with in separate articles. Of special note is Drepanocladus fluitans, a moss found submerged in sluggish streams and pools.