Main Rivers and Ordinary Watercourses: A Guide for Planning

Every river, stream, brook and ditch in England and Wales is legally either a main river or an ordinary watercourse, and the difference decides who regulates it, who maintains it, and whose consent you need before you build near it. Main rivers and ordinary watercourses are managed by different bodies under different laws, so the first question on any site with water on or near it is which of the two you are dealing with.

This guide sets out what each classification means, how to check which one applies to your watercourse, who is responsible for it, and what that means for development.

Get the classification wrong and you can apply to the wrong authority, miss a required consent, and stall a planning application.

What is a main river?

A main river is a watercourse formally designated by the Environment Agency in England, or Natural Resources Wales in Wales, because of its role in regional drainage and flood risk. The designation is recorded on the statutory Main River Map and reviewed periodically.

"Main river" is a legal status, not a description of size. Some are large, well-known rivers; others are modest streams or brooks that carry enough flood risk to warrant Environment Agency oversight.

Because the term is a classification rather than a description, a watercourse with "River" in its name is not automatically a main river, and a small ditch can be one if it has been designated. The only reliable way to know is to check the map, which we cover below.

The Environment Agency and Natural Resources Wales hold the regulatory role on main rivers. They carry out and oversee flood defence work, take enforcement action, and issue permits for works that could affect flow. Changes to the Main River Map happen for two reasons: a designation change, which moves a watercourse into or out of main river status and shifts responsibility between authorities, or a factual change, which corrects the map or reflects a natural change on the ground without altering who is responsible.

What is an ordinary watercourse?

An ordinary watercourse is any watercourse that is not a designated main river. The category covers smaller streams, brooks, ditches, drains, culverts and dykes, and these channels still matter for local drainage and flood risk even though they sit outside Environment Agency control.

Responsibility for ordinary watercourses sits with Lead Local Flood Authorities, the county and unitary councils that lead on local flood risk, and with Internal Drainage Boards in the low-lying areas where boards operate. These bodies regulate work that would obstruct or alter flow, such as culverting, diverting or building over a channel. Day-to-day maintenance, though, usually falls to the riparian owner, the person whose land the watercourse runs through or alongside.

Main rivers and ordinary watercourses: the key differences

The practical differences come down to who regulates the watercourse, whose consent you need, and who maintains it. The table below summarises them.

How do I check whether a watercourse is a main river?

Check the watercourse against the Environment Agency's statutory Main River Map. If the channel is drawn on the map, it is a main river and the Environment Agency regulates it. If it is not on the map, it is an ordinary watercourse and responsibility sits with the Lead Local Flood Authority or an Internal Drainage Board. This single check settles which authority you approach.

For a site in England, open the Environment Agency's statutory Main River Map, search your location, and see whether the watercourse on your site is shown as a main river. The underlying data is also published as an open dataset on the government's environment data platform if you need it in GIS. In Wales, Natural Resources Wales holds the equivalent record. The basis on which the Environment Agency designates a main river is set out in Defra's designation guidance.

Two cautions are worth keeping in mind. The map changes, so check the current version rather than relying on an old extract. And a watercourse can be piped or culverted underground and still be classified, so an absence of open water on site does not mean there is nothing to check.

Who is responsible for maintaining each watercourse?

On a main river, the Environment Agency or Natural Resources Wales manages the larger flood defences, but this does not remove a landowner's own duties. On an ordinary watercourse, maintenance rests mainly with the riparian owner, overseen by the Lead Local Flood Authority or Internal Drainage Board.

If you own land next to, or containing, a watercourse, you are almost certainly a riparian owner, and the law presumes you own the bed and banks to the centre of the channel unless your deeds say otherwise. That carries duties: to let water flow freely, to keep the channel clear, and to maintain any structures you own. These duties apply whether the watercourse is open or piped.

• Ordinary watercourse — report a blockage, pollution or collapsed bank to your Lead Local Flood Authority.
• Main river — report the same problems to the Environment Agency.

What consent do you need to work on a watercourse?

The consent you need depends on the classification. Work in, over, under or near a main river needs a Flood Risk Activity Permit from the Environment Agency. Work that obstructs or alters the flow of an ordinary watercourse needs Ordinary Watercourse Consent from the Lead Local Flood Authority, or from the Internal Drainage Board in board areas. Planning permission does not replace either one.

A Flood Risk Activity Permit is issued under the Environmental Permitting Regulations 2016 and is generally required for works within eight metres of a non-tidal main river, or sixteen metres of a tidal main river or sea defence. It covers activities such as building structures, dredging and altering banks.

An Ordinary Watercourse Consent is required under Section 23 of the Land Drainage Act 1991 before you erect or alter a structure that affects flow, such as a culvert under an access track, a weir or a dam. The Flood and Water Management Act 2010 moved this consenting role to Lead Local Flood Authorities, so applications go to the county or unitary council rather than the Environment Agency. Some authorities call the same thing a flood defence consent.

Neither consent can be granted after the fact as of right: an authority can require unauthorised works to be removed at the applicant's expense.

Why watercourse classification matters for planning and development

Classification shapes the flood risk and drainage evidence a planning application needs, and which statutory consultee reviews it. A flood risk assessment is normally required for development in Flood Zones 2 and 3, and often for larger or surface-water-affected sites in Flood Zone 1. Where the site sits next to a main river, the Environment Agency is the statutory consultee on flood risk; where the issue is surface water and ordinary watercourses, the Lead Local Flood Authority takes that role. In areas covered by an Internal Drainage Board, the board is consulted too.

The mapping is also moving. The Environment Agency's updated national flood data brings smaller watercourses into the Flood Map for Planning that were previously excluded, which means some sites will show flood risk that earlier maps did not. Establishing early whether a site touches a main river or an ordinary watercourse, and building that into the flood risk and drainage strategy, avoids the objections and delays that come from approaching the wrong authority or missing a required consent.

Frequently asked questions

Whether a watercourse is a main river or an ordinary watercourse changes the flood risk evidence, the consents and the authority you deal with. If your site has water on or near it and you need a flood risk assessment for planning, or advice on the right consent and drainage strategy, Unda can help. Get in touch to talk it through with one of our flood risk consultants.