The River Arle, for which Alresford is named after starts in Bishop's Sutton, its' headwaters in the pasture field beyond Hobbs Close and out towards the Ropley Roundabout.

It then passes through the Ford in Water Lane, under the bridge at Bighton Lane and onto Alresford Pond, where it joins the Candover Brook and the Cheriton Stream to form the River Itchen at Ovington.

As a chalk stream, the Upper Itchen Catchment is a priceless natural resource, supporting unique wildlife and sustaining businesses such as watercress and fisheries.

There are only around 210 chalk streams in the world, and 85% of them are in the UK, with a good number in Hampshire. They are an important habitat for wildlife, are fragile and suffer from change very easily.

Key for a chalk stream is that it is not primarily fed from other rivers or from the surrounding hillside, but from the chalk underneath the soil. The chalk is made of up the calcified remains of trillions of microplankton as they died, dropped to the sea bed (when this part of Britain was a shallow sea) and built up over millions of years. Highly porous, the chalk acts as an aquifer and a filter to hold water and chalk streams get their water up from the chalk - which is why it is often very pure and without silt.

Some chalk streams do not run all year round, and this includes our one: the actual permanent water table limit is below the stream bed. Large amounts of rainfall during wet seasons do not affect the stream until a number of weeks or months later as the water gradually filters through the chalk and temporarily raises the water level.

This is called a Winterbourne - a wet winter and spring provides the increased water level that the stream enjoys during the summer. We sometimes see the stream dry up at the Ford during the Autumn if there has been a particularly dry summer, until the next wet set of events eventually filters through again.

Chalk streams, with their fast flowing, clean silt-free habitats are perfect for hosting wildlife and flora - the streams are cool and clear, oxygenated, mineralised with a slightly alkaline acidity and will have a consistent flow (apart from the Winterbourne sections, which may dry up seasonally but return to provide the wet habitat)

These environments are home to a surprisingly large variety of wildlife - geese, herons, swans, egrets, moorhens, bats, otters, water voles, crayfish, fish and a whole variety of aquatic insects for them to feed on - upwings, mayflies, olives, freshwater shrimps, Caddis, stoneflies. Many of these we see in Bishop's Sutton, others are dwindling or becoming rarer as the habitat comes under pressure from climate change and modernisation.

The chalk stream is a delicately balanced ecosystem, very much vulnerable to outside pressures. These pressures that the stream may face are complex, and not the fault of a single factor but the accumulation of many.

Run-off can be from urban areas, farmland and roads. It can be the result of sudden high rainfalls on roads adjacent to the stream, which washes vehicle paint, engine oil, petrol or diesel and even tyre and brake residue that has landed in the road into the stream (that oily sheen you sometimes see on roads when they are wet - that's this stuff). This pollutes the habitat is small ways that gradually accumulates over successive rainfalls.

Sediment washed from fields enters the stream, which would normally have little or no sediment, upsetting the delicate balance of the fauna that thrive on the clean gravel. Where fertilisers are used in gardens or farmland these too can wash into the stream.

Sedimentation can come from run-off but also from bank erosion that is caused by excessive mowing, pollution, overshading, cattle poaching and sometimes the invasive Signal crayfish burrows (our native crayfish don't actually burrow).

Chalk streams are naturally low energy systems - this is not caused by sedimentation in itself. The issue here is that (as low energy systems) the streams don’t always have the power to wash excess sediment downstream. Furthermore, erosion/sediment can further decrease the ‘energy’ of the flow by making the stream overly wide and shallow. Even healthy chalk streams will have slower-flow sections, and indeed this is crucial for some wildlife species (kingfishers can’t hunt in very fast flows, and water voles tend to avoid them too). The key is that we do not want the whole river system to be slow but a mix with powerful water spaces providing clear, gravelly fast moving water giving shelter for aquatic insects and other life - excessive sedimentation smothers the gravel and the wildlife inhabiting it, leading to the loss of higher fish, bird and aquatic mammals that feed off the insects.

Sewage pollution is a big changer of the ecosystem - whether its an acute event or pollution incident or more low level chronic pollution that is less dramatic but builds up over the longer term.

As our village has no mains drains, we all live with septic tanks. Ultimately, the water from those 160-odd houses goes back into the ground and may carry with it chemicals that are harmful and eventually build up and reach the aquifer, and then the stream. Its not just the 'sewage' aspect, but also the nutrients that come from our washing powders, dishwasher cleaner, shower gels and shampoos - nitrogen and phosphates which can cause sewage fungus, cyanobacteria and algal blooms to grow. Also studies of less obvious things like caffeine, oral contraceptives and ibruprofen indicate that these elements can pass into sewgae and harm wildlife. It is important to maintain septic tanks to reduce the impact and consider less harmful chemicals.