The Statutory Main River Map Variations dataset defines proposed changes to the Statutory Main River Map.
Statutory Main Rivers Map defines statutory watercourses in England designated as Main Rivers by Environment Agency.
Watercourses designated as ‘main river’ are generally the larger arterial watercourses. The Environment Agency has permissive powers, but not a duty, to carry out maintenance, improvement or construction work on designated main rivers.
All other open water courses in England are determined by statute as an ‘ordinary watercourse’. On these watercourses the Lead Local flood Authority or, if within an Internal Drainage District, the Internal Drainage Board have similar permissive powers to maintain and improve.
The Environment Agency notifies the public and interested parties of our intentions to make a change to the statutory main river map and decides which watercourses are designated as Main Rivers following a legal process to determine and publish changes.
The change, or variation, to the Statutory Main River Map is either a deletion (also known as a demainment) or an addition (also known as an enmainment).
There are two reasons for a change to the Statutory Main River Map - Designation and Factual.
Designation changes are required when we make a decision to lengthen or shorten the section of a river designated as a 'main river'. These changes will determine which risk management authority may carry out maintenance, improvement or construction work on the watercourse. These changes result also in differing legislation applying to the riparian owner and others with an interest.
Factual changes may be required to update the map to represent the real position of the watercourse. They do not involve any changes of authority or management. Typical examples of factual changes are when: a watercourse has changed course naturally, a watercourse has been diverted or a survey of a culvert shows a different alignment.
A change to the Statutory Main River Map goes through the following stages (identified as Status within the data):
- Draft
- Consultation
- Pending Determination
- Determination
- Appeals
- Pending Appeals
- Pending Implementation
- Implemented (Month and Year) Attribution statement: © Environment Agency copyright and/or database right.
Contains OS data © Crown copyright and database right (2025)
