This upper section is also noted for a number of early bridges, which have survived since their construction in the fifteenth, sixteenth and seventeenth centuries.

The river flows through the South Downs National Park, and is a designated Site of Nature Conservation Importance, in recognition of its value for wildlife.

It supports a wide range of fish, and its upper reaches are the only location in Sussex where native white clawed crayfish can be found.

Following improvements to the River Arun in 1615, which allowed boats to reach Pallingham, they could also navigate part of the Rother, as far upstream as Fittleworth.

Since he owned most of the land adjacent to the river, the precise route of the navigation was not specified, and he was free to improve the channel or make cuts as he saw fit.

Compared to most other canals at the time, the charges for using the navigation were low, as the earl wanted to develop the region rather than make a profit.

[6] During his life, the earl invested some £100,000 in waterways, some in his native county of Sussex, but also in attempts to build a canal from London to Portsmouth.

The boats were hired out by a plumber called William Port, and his business continued to prosper until 1912, when his boathouse burned down.

[8] Another book called A New Oarsman's Guide, published in 1896, suggested that the river could be canoed from Iping to the Arun, a distance of 19 miles (31 km), when there was sufficient water.

After some disagreement, a compromise was reached, under which the bank was repaired and a floodgate was fitted at the upper end of the lock, with both men paying half of the cost.

Lord Leconfield assumed that when the Arun Navigation finally obtained an Act of Abandonment in 1896, his responsibilities for the maintenance of the River Rother had ended.

[10] However, in 1903 heavy rain and floods destroyed the floodgate and part of the adjacent weir, resulting in river levels though the 8th Earl of Egmont's estate dropping by 2 feet (0.6 m).

The case was heard in the High Court, at which it was agreed that the navigation was now useless, but that the two men would share the costs of rebuilding the floodgate, after which responsibility for its maintenance would pass to the earl, who could also dredge the river above the lock.

[11] P. Bonthron, who published a book entitled My Holidays on Inland Waterways in 1916, described a journey down the river that he had made with friends in 1908, in a boat hired from William Port at Midhurst.

[13] The warrant of abandonment was obtained jointly by the estates at Petworth and Cowdray after an Oxford undergraduate called Roger Sellman pointed out that the river was still officially a right of way, and that anyone could therefore offer to pay the appropriate tolls to use a boat on it, and expect the owners to rebuild the locks.

c. 25) were invoked to declare that the navigation was no longer necessary, and despite objections from the River Arun Catchment Board and a canoe club, the warrant was granted on 15 April 1936.

[16] The base flow of the river consists of water from the Lower Greensand aquifer, and from springs along the bottom of the chalk scarp slope.

[20] The entire river, including parts of some of its tributaries, is designated as a Site of Nature Conservation Importance by the local authorities through which it flows, in recognition of its value for wildlife.

Parts of the lower river support the same types of fish, but there are areas, particularly immediately upstream of weirs, where the major species are bream, pike and roach, with chubb, dace and perch on the lowest reaches.

However, some of the small streams in the upper reaches are polluted by discharges of effluent which are not licensed, and there are areas where the water in the aquifer, and hence the river, has raised levels of nitrates, largely caused by agricultural fertilisers.

At Durleighmarsh, a hamlet which forms part of the civil parish of Rogate, it passes the ruins of Durford Abbey, a Premonstratensian monastery situated on the north bank.

[49] Costers Brook, which flows north from springs near Cocking, and then alongside the river for a short distance, joins below the site of the lock.

[54] A modern timber yard and saw mill is located to the north of the lock site,[27] and Lods Bridge, which carries a minor road over the river, dates from the construction of the navigation.

[57] Below the end of the cut, the river is joined by the stream from Burton Mill Pond, which supplied an iron forge built in 1789.

[58] It is crossed by Shopham Bridge, built in the nineteenth century from red brick with grey headers and a parapet in stone, with three segmental arches.

[61] The Tunnel Branch was destroyed by the construction of a water treatment works, and the modern weir near the mouth is much closer to the junction than the lock was.

[63] The organisation is registered as a limited company,[64] and was asked in 2012 to produce a Catchment Management plan by the Department for Environment, Food and Rural Affairs.

It worked with the Arun and Rother Connections (ARC) Partnership and the South Downs National Park Authority to ensure that local opinion was adequately represented in the document.

The reasons for the quality being less than good include sewage discharge affecting most of the river, some physical modification of the channel, the presence of North American signal crayfish, which are an invasive species, and runoff of chemicals as a result of agriculture and land management.

Like most rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE) and mercury compounds, neither of which had previously been included in the assessment.