Guidance

Low risk impounding activities: RPS 302

Updated 25 June 2025

Applies to England

© Crown copyright 2025

This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@nationalarchives.gov.uk.

Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.

This publication is available at https://www.gov.uk/government/publications/low-risk-impounding-activities-rps-302/low-risk-impounding-activities-rps-302

This regulatory position statement (RPS) does not change your legal requirement to have and comply with an impounding licence when you either:

  • construct or change any impounding works on any watercourse
  • cause the flow of any watercourse, including some lakes, reservoirs and ponds, to be obstructed by impounding works

However, the Environment Agency will not normally take enforcement action against you if you do not comply with this legal requirement provided that:

  • your activity meets one of the descriptions set out in this RPS
  • you comply with the conditions set out in this RPS

1. Types of impounding activity this RPS applies to

This RPS applies to the following low risk impounding activities:

  • maintenance works
  • flood risk management measures
  • temporary works
  • works to an existing reservoir dam, including those to a large, raised reservoir
  • habitat enhancement
  • removal or partial removal of small weirs and structures up to 30 centimetres high
  • removal or partial removal of larger weirs and structures up to 150 centimetres high
  • small measurement structures
  • peatland restoration
  • construction of fish easements and fish passes, including those for elver and eel
  • check weirs, boards and dams
  • construction of notches
  • water flow altering structures for ecological enhancement
  • leaky barriers
  • stone dams
  • stop logs to raise water table for wetland or lowland peat restoration

This RPS describes each activity and gives the specific conditions for each. If an activity does not fall under a relevant description, the Environment Agency will not consider it a low risk impounding activity and an impounding licence is required.

You must check if an existing impounding licence covers these activities. If it does, you may need to apply to change (vary) the impounding licence to carry out the intended activity.

This RPS does not change your legal requirement to get other permissions from any other statutory authority, including other functions of the Environment Agency if relevant, such as an environmental permit for a flood risk activity or an abstraction licence.

2. General conditions you must comply with

For the Environment Agency to consider your proposed impounding works as low risk, you must comply with all the ‘general conditions’ in this RPS. This is unless the impounding works are for:

  • ‘peatland restoration’ – in which case general condition 6 does not apply
  • ‘construction of fish easements and fish passes, including those for elver and eel’ – in which case none of the general conditions apply

Condition 1

You must ensure that the works do not cause a deterioration in the status of a water body or compromise the delivery of any relevant environmental objective in:

You can get information on the Water Framework Directive status for an individual water body at: 

Condition 2

You must keep records from the start of the works for a period of 5 years to show that you have complied with this RPS. Records can include:

  • reports and surveys
  • landowner and operator details
  • before and after photographs
  • access agreements
  • technical specifications
  • drawings and plans

You must make these records available to the Environment Agency on request.

Condition 3

You must not cause, or be likely to cause, at any location in the watercourse, harm to freshwater fish, migratory salmonids (salmon and sea trout) or eel resulting from:

  • inhibiting or preventing their upstream or downstream passage
  • disturbance of spawn, spawning fish or spawning area

Condition 4

You must make sure that there is no likely significant effect on any:  

When considering National Network Sites (Special Protection Areas (SPAs), possible SPAs, Special Areas of Conservation (SACs), possible SACs) and Ramsar, the precautionary principle should be used to predict any effects on those sites.

You must not cause or be likely to cause damage to a:

There is guidance on how to search for designated sites and protected species.

Condition 5

You must not have a significant adverse effect on habitats or species included in the list of habitats and species of principal importance in England.

Condition 6

You must not carry out any works within 100 metres of a water body that is classified as of ‘high ecological status’. This is defined by the Water Framework Directive (Standards and Classification) Directions (England and Wales) 2015.

See condition 1 for details on how to access information on the water framework directive status for an individual water body.

Condition 7

You must not derogate an existing lawful abstraction that is a protected right, whether licensed or an abstraction activity exempt from licensing.

You must have regard to:

  • any existing lawful uses
  • other water users, riparian rights or interests

Condition 8

You must not prevent the following statutory authorities from carrying out their legal obligations:

  • navigation authority
  • harbour authority
  • conservancy authority
  • statutory water undertaker 

Condition 9

You must not interfere with the operations of any drainage board for any internal drainage district.

For information on Internal Drainage Boards see the Association of Drainage Authorities website.

3. Activity specific conditions you must meet

As well as the general conditions, your proposed impounding works must meet all the specific conditions for the activity for the Environment Agency to consider them low risk.

Maintenance works

This means maintaining impounding structures, whether it is ongoing or a one-off. 

You must use materials of the same kind as those present in the structure. If use of the materials has been restricted, you must use a suitable similar material.

You must not: 

  • change any dimension of the structure
  • change the design or function of the structure

This activity does not apply to impounding structures that have been taken down or destroyed for half their width or greater or to the phased replacement of the whole structure.

Flood risk management structures

This means managing flood risk by constructing fixed control or passive structures within the channel that only hold back flood flow, for example for flood storage; or erosion protection works for flood risk management.

You must:  

  • allow normal flows to pass downstream unimpeded
  • make sure that where they are currently present or expected to be, fish and eel are allowed to move freely upstream and downstream 

The works must not raise the upstream water level to overflow out of bank under normal flow conditions.

‘Flood flow’ is defined as the point at which water naturally overflows out of bank.

‘Normal flow’ is defined as the water constrained within the channel.

‘Bank’ means any bank, berm, wall or embankment that adjoins or confines any watercourse.

Temporary works

This means works that temporarily impound, impede or divert water during construction or maintenance of a structure. 

You must not: 

  • have impounding works in place for more than 6 months
  • significantly change the downstream flow regime
  • significantly change the water level upstream of the impounding works 

Works to an existing reservoir dam, including those to a large raised reservoir

This means either:

  • changing, moving or constructing a spillway on an existing reservoir dam
  • installing a wave wall on an existing reservoir dam

You must not change the:

  • upstream impounding level
  • downstream flow regime

‘Spillway’ means a structure that, when a reservoir is full, enables floodwater to pass safely and in a controlled way, over, around or through a dam. A spillway can be:

  • part of a dam
  • next to a dam

A ‘large, raised reservoir’ is as defined by the Reservoirs Act 1975 and can hold 25,000 cubic metres or more of water above the natural ground level.

Habitat enhancement

This means placing stones, logs, woody material, or other suitable materials, for habitat enhancement across part of the width of the watercourse.

You must use materials that are found naturally where the works will take place, or a suitable alternative.

The works must not occupy more than half of the cross-sectional area of the channel.

Removal or partial removal of small weirs and structures up to 30 centimetres high

This means removing all, or part of, a weir or structure from a watercourse.

The weir or structure to be removed must not be more than 30 centimetres from the upstream base of the structure to the crest level at the lowest point.

You must not have a significant adverse effect on downstream habitat through the creation of silt mobilisation.

Removal or partial removal of larger weirs and structures up to 150 centimetres high

This means removing all, or part of, a weir or structure from a watercourse.

The weir or structure to be removed must not be more than 150 centimetres from the upstream base of the structure to the crest level at the lowest point.

You must have written agreement for the works from all landowners, riparian interests and other water users, including the owner of the weir or structure, in the length of the watercourse affected by the works.

The works must not:

  • as a result of lowering the water level, create a new upstream impoundment for example expose a pipe or other structure, that inhibits or prevents the upstream or downstream passage of fish or eel
  • worsen upstream or downstream passage of fish or eel at an existing upstream impoundment
  • cause any upstream infrastructure to be undermined

You must not:

  • undertake any works on a weir or structure that facilitates a lawful upstream abstraction without written agreement from the operator of the abstraction
  • undertake any works on a weir or structure that controls the flow of water into another watercourse, or another part of the same watercourse
  • have a significant adverse effect on downstream habitat through the creation of silt mobilisation
  • undertake any works on a weir or structure at the freshwater and tidal limit of a watercourse
  • adversely affect any water-dependant habitats such as a floodplain, wetland or groundwater dependent habitats
  • impact the operation of a hydrometric gauging station operated by the Environment Agency, or other organisation for example a statutory water undertaker or a navigation authority, without the agreement of the operator
  • carry out any works on any weir, or structure that is a scheduled ancient monument, without the consent of the appropriate authority

Small measurement structures 

This means installing small water level, water flow or other types of measurement structures that span and impede the watercourse. 

The structure must not be: 

  • more than 30 centimetres in height from the upstream base of the structure to the crest level at the lowest point
  • in place for more than 12-months in a watercourse where salmon, sea trout or brown trout are currently or expected to be; or 36-months in all other watercourses

This does not include:

  • a measurement structure that is required as a condition of an impounding or abstraction licence; or that is essential to assess compliance with a licence condition 
  • ancillary measurement equipment such as a gauge board; or equipment which is fixed to a support or to the bank, such as a sensor in a stilling tube or cable suspended monitoring 
  • measurement equipment which sits on the bed and banks of the watercourse and that does not significantly change the water level upstream 

Peatland restoration

This means blocking gullies, grips or drainage channels for the purpose of re-wetting peatland fens and peat habitats, such as blanket bog or raised bog.

You must use peat from where the works will take place. Where this is not possible a suitable alternative can be used.

The works must not happen where fish (excluding eel) are currently present or expected to be.

Construction of fish easements and fish passes, including those for elver and eel

This means constructing fish easements and fish passes, including those for elver and eel, on existing impounding works. 

You must not start construction until your design has been approved by the Environment Agency to meet the requirements of the Salmon and Freshwater Fisheries Act 1975 and or The Eels Regulations 2009.

Find out how to get approval for a fish or eel pass. Please note the fish pass approval form and guidance document also covers eel and elvers.

Check weirs, boards and dams

This means works installed in the bed of the watercourse to hold bed substrate in place. 

The works must not: 

  • cause a change in water level 

  • protrude above the final intended bed substrate level
  • use plastics 

You must use natural materials such as wood or stone, unless the channel is made entirely of unnatural materials such as concrete, then these materials can be used. 

Construction of notches

This means notches in an existing impounding structure to improve fish passage. This includes constructing a single notch or multiple notches in an impounding structure.

You must ensure that any notch being placed in a weir or other impounding structure is effective at enabling fish to move upstream and downstream of the structure safely. An effective notch is one that:

  • limits the need for fish to jump 
  • is of depth and elevation that reduces the speed of water flowing through it to allow fish to swim upstream 
  • has sufficient depth of water downstream of the structure to allow fish to easily approach the structure
  • prevents damage occurring to fish 

You must ensure that the: 

  • notch or notches are of a combined width of no more than 100 centimetres 

  • notch or notches are no more than 40 centimetres in depth 

  • bottom of any notch is set at or below the minimum downstream water level 

  • minimum depth of water immediately downstream of the notch is at least twice the depth of the notch  

  • notch or notches do not significantly change the upstream water level 

You must follow the criteria for the appropriate fish species groups, as listed. If more than one species group is present, you must follow the criteria that meet the requirements of all the species groups present.

Coarse fish, brown trout, grayling and small sea trout: 

  • notch width is 30 centimetres or greater
  • notch depth is between 15 and 30 centimetres  

Salmon and large sea trout:

  • notch width is 60 centimetres or greater
  • notch depth is between 25 and 40 centimetres 

Water flow altering structures for ecological enhancement

This means the installation of structures within the watercourse that alter the flow distribution, direction or velocity of the flow across all or part of the width of the watercourse. For example, berms, deflectors and woody dams.

Where fish and eel are currently present or expected to be, the works must not occupy more than two-thirds of the cross-sectional area of the natural channel.

Where fish and eel are not currently present or expected to be, the works can occupy the entire width of the channel.

The works must not: 

  • change the location where the watercourse enters and exits from the site

  • change the water level outside that which would naturally occur at the site 
  • prevent water entering or leaving the site
  • use plastics

The works must:

  • be for the purpose of watercourse naturalisation and or ecological improvement 

  • use materials that are found naturally where the works will take place, or a suitable alternative material 

  • make sure that where they are present, fish and eel are allowed to move freely upstream and downstream  

Leaky barriers

This includes structures made from natural materials, such as leaky woody barriers.

You must:   

  • ensure the structure is suitably secure 

  • where more than one log is used, include sufficient gaps within the works to allow water to pass through the structure  

  • ensure that low to medium flows are allowed to pass downstream unimpeded 

  • make sure that where they are currently present or expected to be, fish and eel are allowed to move freely upstream and downstream

  • use materials that are found naturally where the works will take place, or a suitable alternative material 

The works must not:   

  • be placed on a watercourse that is more than 5 metres wide from   bank top to bank top 

  • cause excessive scour to bed or banks of the watercourse that would undermine the structure

  • be placed within 20 metres upstream or downstream of man-made infrastructure in the watercourse, such as a bridge or a culvert 

Stone dams

This includes structures made from stone designed to be permeable and to slow water flow upland headwaters. 

You must:  

  • use stone that is found naturally where the works will take place, or a suitable alternative stone 

  • use stone that does not negatively impact water quality, pH or visual amenity  

  • ensure stone is clean prior to use 

You must not:  

  • use any material classed as waste

  • use concrete or other fixing agent to fix stones in position  

The works must not happen where fish (excluding eels) are currently present or expected to be.

Stop logs to raise water table for wetland or lowland peat restoration

This means structures located at regular intervals from the start of a drainage or watercourse system to raise the level of the water table in the surrounding area.

The works must not: 

  • be more than 500 metres from the start of the drainage or watercourse system 

  • take place in a watercourse where salmonids (brown trout and salmon) are present 

  • take place in a chalk stream or at a spring head 

  • facilitate a primary abstraction into a managed wetland system 

You must make sure that where they are currently present or expected to be, fish and eel are allowed to move freely downstream.

4. Things to note

The government has consulted on abstraction and impounding activities moving into the environmental permitting regulations. This RPS relates to activities that the Environment Agency considers are potentially suitable to be either an exclusion or an exemption (subject to approval) under those regulations.

This regulatory position does not apply to any other legal requirements.

Work to create new structures in watercourses or alter existing ones may require permission from other authorities to manage their impacts on flood risk and land drainage. Works affecting main rivers and their flood plains may require an environmental permit from the Environment Agency. If you are carrying out work to an ordinary watercourse (any watercourse that is not specifically defined as a ‘main river’), then you should contact the lead local flood authority (upper tier or unitary authority) or internal drainage board (if there is one).

If you cannot comply with all the relevant conditions in the RPS, you must apply for an impounding licence. This means that the risks from the proposal at the specific site need more careful consideration through the assessment of an application. In these cases, work must not start without a licence.

You can apply for an impounding licence instead of relying on this RPS if you prefer.

5. When you must check back

The Environment Agency intends to review this RPS by 25 June 2028.

The Environment Agency can withdraw or amend this regulatory position before the review date if they consider it necessary. This includes where the activities that this RPS relates to have not changed.

This RPS remains in force until it is removed from GOV.UK or is otherwise identified as having been withdrawn.

You can subscribe to email updates about this RPS. These will tell you if the RPS has changed and when it has been withdrawn.

6. If you cannot comply with this RPS

If you operate under this RPS but can no longer comply with it, you must:

7. Contact the Environment Agency

If you have looked at this RPS and you are not sure if your proposal needs an impounding licence, you can get advice using the Environment Agency’s enhanced pre-application service. 

If you have any questions about this RPS, email wrregulation@environment-agency.gov.uk with RPS 302 in the subject.

Back to top