Bacteria - Water Quality Testing - Water Quality Trends - Nitrates - Chemicals and Metals - Microplastics

Chichester Harbour Water Quality

View the latest water quality sampling results.

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 not however in a pristine state and are heavily impacted by human activity.

Recognising the imperative of good water quality, the Conservancy has been working for many years to understand the pressures and to strive for improvements. 

The principal parameters we are focussed on are bacteria, nitrates, chemicals & metals, and microplastics.


Of most immediate concern to Harbours users is the level of bacteria, with the obvious links to human health. These 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.

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.

Water Quality Testing

Most of the time, Harbour waters do not appear unduly impacted from high levels of bacteria from these sources. However, after heavy rain bacteria levels can increase.  In these circumstances the increased flows from run-off water adding to the wastewater can lead to the WWTW’s storm discharging. When the amount of effluent reaching the WWTW’s exceeds its capacity to treat it, excess flow is diverted to a storm tank. If that fills, the overflow goes through a 6mm mesh screen before being discharged to the Harbour. In the case of Apuldram, the storm discharge also goes through a UV disinfection process to kill the bacteria. Storm discharges can lead to increased levels of bacteria. 

It is noteworthy that these storm discharges can continue for significant periods in the Chichester area as the water table becomes higher than the wastewater pipes leading to ingress and increased flows to the WWTW’s.

To determine how Chichester Harbour is impacted by these inputs, in 2007 the Conservancy joined forces with Chichester District Council to test the water quality at 11 different sites around the Harbour. These are undertaken every two weeks during April to the end of October and monthly in the winter.

In 2021, further to discussions with the Chichester Harbour Federation, the timings of water samples taken around the harbour were changed. Until now, due to the very tidal location of some of the sample sites, water samples were taken as the tide rises to allow a single vessel to reach all sites within one tide. To further gauge the effect of storm water discharges on water quality, samples are now taken approximately 2 hours after high water, on the ebb tide. To accomplish this, two vessels cover the west and east side of the harbour respectively, starting with the highest tidal locations such as north of Dell Quay and the Emsworth Jetty and working back towards Itchenor. The samples are kept refrigerated at the Harbour Office overnight, before being delivered to CDC the following day where a courier then takes the samples for analysis at the Porton Food, Water and Environmental Laboratory.

While this new system will be regularly reviewed, to create a comprehensive data set the new sample schedule will continue for the foreseeable future.

In addition to the change of schedule, a twelfth sample site (Northney Beacon) was established in April 2021 to ascertain any effect that the Budds Farm WWTW (sited in Langstone Harbour, approximately 1 mile NW of the Langstone bridge) may have on water quality in Chichester Harbour. In December 2021, two existing sample sites were changed to better monitor the effects of specific WWTW outfalls. The Thorney Island Slipway site was moved north to the Great Deep Sluice, and the Itchenor Jetty site was moved to the entrance to Furzefield Creek.

Although Chichester Harbour is not a designated bathing water, we compare the results with standards from the Bathing Water Directive. You can view historical results on the Chichester District Council website, the most recent water quality results are shown here.

Sample Site Map

Water Quality Trends

We have undertaken thousands of water quality tests since starting our testing regime in 2007 and produced in-depth analysis of the long-term trends in water quality for 11 of the sites tested. The Northney Beacon site was added to the regime in April 2021, trend analysis from this site will be added once more data has been gathered.

Please click the links below to view the analysis of the individual sampling sites:

  1. Emsworth Jetty
  2. East Head
  3. Thorney Island SC Slipway (site relocated to Great Deep Sluice in December 2021)
  4. Deep End
  5. Cobnor Activities Centre Slipway
  6. Bosham Quay
  7. Itchenor Jetty (site relocated to the entrance to Furzefield Creek in December 2021)
  8. Chichester Marina Beacon
  9. Chichester YC Slipway
  10. Dell Quay
  11. North of Dell Quay
  12. Northney Beacon (new sample site added April 2021)


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.

Further Information

Telemetry at the WWTWs records actual storm water discharges and email notification of these can be received directly from Southern Water, visit for further information.

Further information, water quality testing results, and environmental health advice are available on the Chichester District Council Website.


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. For further details please see our RedPol pages here.


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.

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