The Reservoirs Act 1975 defines a high risk reservoir as one which NRW as the appropriate authority “think that in the event of an uncontrolled release of water from the reservoir, human life could be endangered.” This definition places a duty on us to consider only the consequences of flooding, not the likelihood of a reservoir failing.

The law does not define any reservoir as low risk, but we recognise that some reservoirs, if they should fail, will be unlikely to harm human life. Owners and operators for these ‘not high risk’ reservoirs will benefit from reduced regulation and will not have to employ civil engineers to supervise and inspect their reservoirs.

We use a 3-step process for determining a reservoir’s risk designation:

  1. We will review the information we have for the reservoir and may seek the opinion of an independent All Reservoirs Panel Engineer to establish the consequences of a flood caused by the failure of the reservoir
    1. If there is clear evidence that we consider human life would not be endangered, we will write to the undertaker to confirm we do not consider their reservoir to be high risk
    2. If there is evidence that human life would be endangered, or we have doubt, we will provide the undertaker with a notice of provisional designation as a high risk reservoir
  2. Our notice of provisional designation provides the opportunity for the owner or operator to either accept our provisional designation or to provide further evidence to inform our decision. This period for representations will be open for three months
  3. Following the period allowed for representations we will consider any new information provided by the undertaker and we will either confirm or alter our provisional designation. We will call this our final designation


If you remain dissatisfied with our final designation you may appeal our decision. Details of how to do this will be included with our notice of final designation. An appeal will determine whether our designation is valid, or not.

Not-High-Risk Reservoirs

If we have written to you and confirmed your reservoir as 'not high risk' it means that we have reviewed sufficient evidence to conclude that human life would not be endangered if there were an uncontrolled release of water from your reservoir. This means you are no longer legally required to appoint a supervising or inspecting engineer. However, your reservoir is still registered as a large raised reservoir and will remain on the register of large raised reservoirs. You must still comply with the other requirements of the Reservoirs Act 1975 and you must contact us if:

  • Any of the registered information changes, for instance if ownership changes
  • An incident occurs
  • You wish to increase or decrease the capacity of the reservoir
  • You wish to abandon or discontinue the reservoir

You may request a review of our risk designation, or we may start a review, at any time if we consider it necessary. A not-high-risk reservoir may still pose a threat to people, property and the environment for which you have a duty of care.

High-Risk Reservoirs

If we send you a notice telling you we consider your reservoir to be a high risk reservoir, you must fulfil all the obligations required of you under the Reservoirs Act.  The most important actions you will need to take are:

We also recommend that you write an onsite flood plan.

Our risk designation does not affect any other permissions or obligations that relate to your reservoir. Such topics may include, amongst others:

  • Environmental Permits for abstraction or discharge
  • Fishery licensing
  • Health and Safety at Work Act
  • Planning applications
  • Scheduled Ancient Monument consent
  • Listed Building consent
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