Untreated sewage from boats can spread gastroenteritis; contaminate shell fish beds and use up vital oxygen in the water. Human waste also contains phosphorous and nitrogen which both increase the levels of algae and reduce water clarity. Chemicals such as chlorine, formaldehyde, ammonium and zinc compounds, used to disinfect breakdown and deodorise waste, are toxic to marine life.

Overboard discharge is prohibited on most inland waterways and local byelaws exist for tidal and coastal waters.

As the Recreational Craft Directive states that provision must be made for holding tanks in new build boats, more and more boat owners are having them fitted and using them. Marinas may find an increased demand for pump out facilities from their berth holders in future.

Whilst installation may be seen as prohibitively expensive, some operators make charges to pump sewage ashore which enables them to recoup some of the costs.

The Green Blue promotes its 'Love Where You Sail' initiative in partnership with the Environment Agency to encourage responsible discharge of black water by boaters. Take a look.

Love Where You Sail