Summary of the possible effects of wastes managed within ports and harbours and suggestions for means of avoiding, minimising and addressing them

(Ben = Beneficial, Min = Minimal, Adv = Adverse)

Port and Harbour Operations

Potential issues, key processes & potential impacts


and comments



Potential impacts on marine SACs




Possible means of avoiding, minimising and addressing impacts

Issue: Oil discharges/spills

Key process: Toxic contamination

Non-toxic contamination (organic enrichment & turbidity)

Physical damage (smothering)

Potential impact: Accidental and operational oil spills in ports and harbours can cause disturbance, damage and/or death to marine habitats and species, including marine mammals, birds, benthic communities, fish and saltmarsh. Oil can cause the following impacts on marine wildlife and habitats:

  • physical disturbance due to smothering and direct toxic effects,
  • organic enrichment possibly causing localised removal of oxygen,
  • contamination of sediments can lead to the storage of persistent toxic oil constituents, such as heavy metals.

Clean up activities may also cause impacts on wildlife:

  • Dispersants prevent and minimise the spread of oil, but also promote its penetration into the sediments, potentially affecting fish and other sensitive intertidal communities.
  • Physical damage caused to benthic plants and animals during clean up operations.

Although relatively rare, major accidental oil spills do happen and can potentially cause a major impact on marine SACs. However, the majority of oil spills reported in ports and harbours are small and result from operational activities. The potential impacts from oil spills depend upon the type and quantity of oil, location of spill, hydrodynamic conditions, proximity to sensitive marine habitats and species, and, where appropriate, the effect of emergency response. In industrialised estuaries and bays it is difficult to distinguish between the effects of the numerous sources, and research is needed. Oil pollution prevention is cheaper in the long-term, than attempts to clear up.





















Port waste management planning and provision of adequate waste reception facilities for oily wastes.

Oil spill contingency planning according to regulations and guidelines and effective response to avoid and minimise effects.

Identify areas where the use of dispersants presents little or no concern, and areas containing sensitive marine features where their use should be avoided, unless there is greater risk of oil pollution damage on marine features.

Ensure careful clean-up operations in the vicinity of sensitive animal and plant communities, seek advice from countryside conservation agencies where appropriate.

Issue: Garbage disposal & litter

Key process: Physical damage (abrasion & smothering)

Potential impact: Marine mammals and birds can become entangled in or ingest plastic litter which can lead to injury or fatality.

Ship generated garbage may cause localised smothering of benthic communities. Garbage and Litter

It is difficult, although possible, to distinguish the effects due to ship’s litter and other sources of marine litter. Impacts depend on amounts and types of litter. Problems are mostly associated with persistent plastics. Entanglement and ingestion of plastic litter by birds and mammals occurs in UK waters, but the incidence rate is unknown.

Smothering is only likely to be localised and temporary.












Port waste management planning and the provision of adequate waste reception facilities for garbage wastes.

Encourage the responsible management of waste, including minimisation and recycling, at the point of generation on ships, reception in ports/harbours, transportation and disposal.

Ensure port/harbour users that report large pieces of floating garbage.

Consider the collection of marine litter, particularly plastics, where considered necessary.

Issue: Sewage discharge from recreational craft

Key process: Non-toxic contamination (organic/nutrient enrichment & turbidity)

Toxic contamination

Potential impact: Discharges of high concentrations of sewage may cause a localised deterioration in water quality, which may result in oxygen depletion, increased suspended solids, nutrient enrichment and increased risk of algal blooms which may disturb animals and plants. Chemical additives in portable toilets and holding tanks (including chlorine, ammonium & zinc) are toxic to marine life. Generally the impacts associated with sewage discharged by recreational craft are minimal in comparison with those which arise from the far greater amounts discharged from land-based sources. Impacts are generally localised and temporary.

Potential impacts depend on numbers of vessels, amounts of sewage, water quality, temperature and depth, tidal movement and proximity of sensitive species. Greatest effects are likely to occur when many vessels congregate in enclosed areas or shallow water with little or no tidal exchange in summer and autumn. In some cases nutrient enrichment from sewage may increase productivity, the benefits of which are likely to be seen in higher organisms in estuaries or bays, such as feeding bird populations. However, despite small possible incidental benefits, this should not be to the detriment of water quality in the site.





Consider providing onshore reception facilities for pumping-out sewage wastes.

Encourage use of shore-side toilet facilities, holding tanks where fitted and disposal of waste at pump-out facilities, and while underway as far offshore as possible in areas where strong currents ensure dispersion and dilution.

Discourage/prohibit discharge of sewage wastes where doing so would harm marine features.

Issue: Discharge of ballast water

Key process: Introduction of non-native


Potential impact: The introduction of non-native animals and plants in ships ballast water may have a range of effects, from undetectable to the complete detriment of native communities. Species introduced to the UK from ballast water include various bloom forming phytoplankton, a number of fouling organisms, marine benthic animals that compete with native communities and an American cordgrass Spartina species, which crossed with the native species to form common cordgrass that has since spread throughout Britain, replacing native saltmarsh species.

In the UK, around 80% of introduced species have no effect, however 20% from a number of sources do have some effect on native communities, in many cases causing disturbance and damage. The introduction and potential effects of harmful non-native species are highly unpredictable, but can be very serious.





Comply with IMO guidance and support MCA in encouraging shipowners to comply with IMO guidance.

Inform local agents and ships of areas where uptake of ballast water should be avoided.

Encourage the exchange of ballast water at sea, where it is considered safe to do so, which will be regulated by the MCA

Discourage / prohibit the unnecessary discharge of ballast water in the port and harbour area, where appropriate.

Next Section