Water Quality

Bacteria | Waste Water Treatment Works | Water Quality Testing | Shellfish | Nitrates | Chemicals & Metals | Microplastics

Good water quality is essential for the health of the Harbour; particularly for the wildlife that depend on it and the people who enjoy it.

Harbour waters are heavily impacted by human activity. As well as regularly testing the water quality within the harbour, Chichester Harbour Conservancy is working to understand the pressures and to strive for improvements. We support a number of research projects into pollution and water quality within Chichester Harbour.

Our policy on water quality, noted in our Management Plan, recognises that the water of Chichester Harbour needs to fulfil a conservation value as well as support recreational use of the harbour.

Work continues to manage sources of water pollution from harbour users. Waste reception facilities are provided and oil spill response preparedness maintained.

The principal parameters we are focussed on are:


Water Quality Testing

Chichester Harbour Conservancy, in conjunction with Chichester District Council monitor the quality of the water within the Chichester Harbour. Samples from 12 locations in the harbour are collected and tested twice a month during the summer months and monthly throughout the winter.

Although there are no regulatory standards for this area of water, the EU Bathing Water Standards are used as a guide. Chichester Harbour is not a designated bathing water site, however the test results can be viewed as an indicator of potential pollution levels at the time of testing.

Historical results are available on the Chichester District Council website.

Bacteria enter the Harbour from several sources:

Wastewater Treatment Works (WWTW)

There are 3 wastewater treatment plants that discharge directly into the Harbour at Apuldram, Bosham and Thornham. These were upgraded in April 2008 so all treated sewage now receives Ultraviolet (except Thornham) and bacteriological treatment, and some of the nutrients are removed before the effluent is discharged.

In addition, storm discharges from Lavant WWTW can impact the Harbour via the River Lavant, as can Southern Water activity pumping from the surcharged pipes into the River Lavant to take pressure off the wastewater system in upstream villages such as East Dean. Storm discharges from Budds Farm WWTW in Langstone Harbour are also likely to impact to some degree.

Associated with Southern Waters sewage infrastructure, there are several pumping stations and combined sewage overflows, that can also discharge during storm conditions.

Telemetry at the WWTWs records actual storm water discharges and email notification of these can be received directly from Southern Water. Further information, water quality testing results, and environmental health advice are available on the Chichester District Council Website.

Other Sources

A number of streams flow into the Harbour, many of which will pass through fields grazed by cows, sheep and horses. There will also be run-off from land around the Harbour during heavy rain. Yachtsmen and other Harbour users will also have some impact.  

Private package treatment plants and outputs from septic tanks from older properties contribute further.


Chichester Harbour is classified as a shellfish water and while the bacteriological quality of the water tested is generally excellent when measured against the Bathing Water Directive standards, E.coli appears to show up more readily in shellfish, filter feeding on the seabed. Oysters are tested every month by Chichester and Havant Environmental Health departments and oysters usually test at grade B or Grade C which means they would require further treatments before they were fit for human consumption. Higher spikes are also found on occasion.


Nitrates enter the Harbour from a number of sources but principally from agricultural run-off and from WWTW’s. Taking the Harbour as a whole, most nitrates enter from the wider Solent with significant inputs from the rivers Test and Itchen. It is notable however that during wet winters nitrate levels (dissolved inorganic nitrates DIN) are considerably higher at the tops of the channels and in the case of Fishbourne Channel 600% higher than samples taken at Fishery Buoy near to the Harbour entrance. This points to significant inputs from storm discharging WWTW’s, as well as inputs from the streams, which would include agricultural run-off.  

Excessive nitrates lead to the growth of macroalgal weed and because of this the Harbour is classed as eutrophic. Macroalgal weed can be seen throughout the Harbour, particularly in summer as the green mats of weed that blanket intertidal areas. This has several impacts; preventing birds from feeding, if it builds sufficiently it can exclude oxygen from the mud below and kill off the invertebrates, and smothering saltmarsh, causing it to die back.

Saltmarsh is an extremely important habitat, and in addition to supporting wildlife, is an extremely effective sequester of carbon. Saltmarsh can also respond to sea level rise in the right conditions, able to increase in height by up to 6mm a year forming a very effective sea defence. Of great concern, Chichester Harbour has lost 58.8% of its saltmarsh since 1946, to a mixture of excess nitrates, coastal squeeze caused by sea defences and increasingly, by sea level rise.  

Excess nitrates also impact negatively on seagrass beds, another important habitat in the Harbour providing protection to juvenile fish and seahorses, and another highly effective sequester of carbon. Areas of highest nitrates see the greatest loss of saltmarsh and seagrass.

Chemicals and Metals

Harbour waters and sediments contain a mixture of compounds and heavy metals; a mixture of industrial legacy from the wider area, inputs from WWTW’s, run-off and Harbour activity. The Environment Agency test a number of parameters. An increased focus on new substances being tested for and improved techniques has recently identified, in common with many other areas, high levels of PBDE – Polybrominated diphenyl ethers, used in flame retardants, electrics, foams and textiles. Also, high levels of mercury and it’s compounds. Raised levels of copper and zinc are also identified associated with boating.

Rapidly expanding consumer markets and industrial manufacturing cause new chemicals to enter the aquatic environment every year, and among them, a number of Endocrine Disrupting Contaminants (EDCs) with the potential to affect aquatic wildlife.

There is strong evidence that EDCs interfere with the hormones in aquatic organism leading to a number of different impacts.

Concern exists about several contaminants frequently detected in local estuaries, such as phthalates, polyfluoroalkyl and perfluoroalkyl substances (PFASs), homosalate, flame retardants and several pharmaceuticals. These compounds are persistent and likely to bioaccumulate, however evidence regarding their biological impact is limited.

Concern about the effects of EDCs has arisen in Chichester Harbour because of observations of local oyster population declines in the past decade. Only a few toxicological studies have been conducted so far, pointing towards endocrine pathologies and skewed sex ratio.

To facilitate greater understanding of this issue, the Conservancy is a partner in the Interreg funded Reduce Pollution (RedPol) project, which seeks to identify substances that have significant negative impacts on aquatic life.


Microplastics (generally plastic pieces less than 5mm in size) and microfibres have a growing and significant presence in today’s environment. Research by the University of Portsmouth has looked at the prevalence of microplastics and nurdles and found them to be widespread throughout the Harbour with particular concentrations at the Harbour entrance and on lee shores for the prevailing winds. The University of Brighton has studied microfibres extensively in the Harbour’s waters and sediments and have identified 10,000 microfibres per litre on the surface of the Harbour, they also identified tiny shards of glass reinforced plastic (grp) in oysters in the Dell Quay area. Research is ongoing to understand the impact of these findings and also to find materials that will be able to remove some of the microfibres from the Harbour environment.