The River Whitewater rises at springs near Bidden Grange Farm between Upton Grey and Greywell in Hampshire, England.

Its headwaters flow over chalk and there is little pollution making the River Whitewater rich in wildlife.

[2] The settlements of Greywell, North Warnborough, Hook, Hartley Wintney, Rotherwick, West Green, Mattingley, Bramshill and Heckfield lie on the River Whitewater.

The Whitewater rises as a series of springs and channels near Bidden, in the Odiham Fen Site of Special Scientific Interest (SSSI).

The underlying chalk aquifer supplies base-rich water which encourages the growth of fen vegetation, notably lesser tussock-sedge and giant spearmoss.

[5] There are further springs and channels as the river heads north eastwards, to reach Deptford Bridge.

[13] Next comes Poland Mill, a large two-storey 18th century rectangular building, which originally had six water wheels, of which one with a cast iron frame remains.

[14] The next section, which follows a more northerly course, is marked by bridges carrying the M3 motorway, the South West Main Line railway and the A30 road over the river, to the east of Hook.

They date from the 17th and 18th centuries, and both now form part of a single house, in which the huge timbers of the mill building are still visible.

[18] The main tributary of the Whitewater is the River Hart, which joins on the right bank, before the combined flow passes under Heckfield Bridge.

Its water is derived from an underlying chalk aquifer, as a series of spring in the Odiham Fen SSSI.

As the river approaches Hook, the geology alters, with the underlying chalk replaced by clay and gravel substrates.

This is largely due to the number of weirs that have historically been associated with milling, making it difficult for fish to move upstream and fragmenting the habitat.

In 2012 the Wild Trout Trust carried out a survey of the 1.9-mile (3.1 km) section from below Hook Mill to Dipley Bridge, just above Dipley Mill, because the Whitewater Syndicate who have managed that part of the river as a fishery for 30 years were concerned that river flows seemed to be reducing, and that the growth of aquatic plants was declining.

Lack of plants resulted in fewer flies, a major source of food for trout, and a general decline in the fishery.

At the downstream end, the effects of Dipley Mill are that there is a long section of deep, slow-moving water, which is not ideal for trout.

There were sections where weed growth was affected by a lack of light, caused by large Alder trees growing on the banks.

Trout need dappled shade, and selective coppicing of the trees would result in improved weed growth.

[24] A number of low weirs had been built across the stream bed, in an attempt to improve water levels, but had resulted in slower flows depositing fine silt behind them, reducing their effectiveness.

The report recommended that some of them should be removed, and replaced with large woody debris on the verges of the channel, to create faster-flowing water and help to scour silt from the bed, resulting in better conditions for plants, invertebrates and fish such as trout that prefer faster flows.

This depends on the river bed being composed of gravel, and fast flows, and is a typical chalk stream plant.

There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish.

Reasons for the quality being less than good include discharge from sewage treatment works; runoff from agricultural land; physical barriers such as weirs and impounding of the water which prevent the free migration of fish and other species; and the presence of the North American signal crayfish, an invasive species.

Some of them were owned by Robert the Parker around 1200, from whom King John took 20 acres (8.1 ha) on which to build Odiham Castle.

It was described as a large fulling mill at that time, and produced woolen and worsted cloth, while weaving was carried out in the local cottages.

At some point an oil engine was used to power the machinery, which included four pairs of stones on a hurst frame, and another two on the second floor.