What is a watercourse?

What is a watercourse?

One of the questions which I am most frequently asked in my interactions with construction sector professionals is: what exactly is a watercourse?

To answer the question, it really depends on the context and where you are in the UK.

To start, The Rivers (Prevention of Pollution) Act 1951 defines a water course “as any channel through which water flows” and it also includes “those rivers which are dry for part of the year”.

However, that’s not really the answer they are looking for, often the requirement is for engineering or pollution prevention.

England and Wales

In England and Wales, in an engineering context, there are two types of water course: main rivers and ordinary watercourses.

Main river

A main river is defined on an Environment Agency/Natural Resource Wales map.

Ordinary watercourse

An ordinary watercourse is every river, stream, ditch, drain, sluice, sewer (other than a public sewer) and passage through which water flows and which does not form part of a main river.

They do not necessarily have to transport water. Some act purely for storage to prevent water from collecting elsewhere and seasonal flows may also make watercourses appear dry. In times of heavy rainfall these play an important role in accommodating flood water.

Authorisations may be required from statutory bodies for engineering works on any of the water courses mentioned above.

Pollution control

With regards to pollution control, the Environment Agency recognises the need for controls when discharging pollutants to what they define as surface waters, which includes “rivers, streams, estuaries, lakes, canals or coastal waters” as well as discharges that may impact on ground water.


In Scotland in an engineering context, notification to the environmental authority, in this case SEPA, is not necessary if the surface water does not feature on a 1:50,000 scale map, you do however, still have to abide by the General Binding Rules for that activity. If it does feature, a registration, simple or complex licence is required for certain activities.

In a pollution control context SEPA reference the water environment which includes all surface and groundwater, rather than the term “watercourse”.

For definitive guidance about what constitutes a watercourse and what steps should be taken to protect it, professional advice is a must.


If you would like some professional advice on this subject, don’t hesitate to get in touch. We have a lot of experience in this area and happy to share it.

-This article was written by Naturally Compliant Director, Simon Knott.