The Fish Disco: When Infrastructure Dances

I discovered something called the Fish Disco — a term I first came across on Twitter, and one that sounded more like a novelty installation than a piece of national infrastructure.

In reality, the Fish Disco is a highly sophisticated environmental protection system at Hinkley Point C in Somerset, one of the most advanced nuclear power stations currently under construction anywhere in the world. Despite its playful nickname, this is serious engineering: a £700 million marine mitigation system designed to protect fish and wider marine ecology from the impacts of cooling-water intake.

EDF has described Hinkley Point C as incorporating more marine-life mitigation than any other power station globally — a claim that signals both the project’s ambition and the level of scrutiny it has faced.

This presentation aims to demystify the Fish Disco: where the name comes from, how the system works, and why such an extensive intervention became necessary. More broadly, it offers a lens through which to explore familiar themes in the built environment — trade-offs, regulation-driven innovation, and the challenge of reconciling long-term environmental protection with national growth and energy security.

Background

The UK faces a dual challenge: rising demand for housing and infrastructure alongside the urgent need to decarbonise energy production. Nuclear power, long established across much of Europe as a reliable, high-capacity, low-carbon energy source, plays a key role in addressing both energy security and climate targets.

In the UK, nuclear power is subject to an especially risk-averse regulatory culture, shaped by historical incidents and public sensitivity. As a result, projects like Hinkley Point C are held to some of the most stringent safety standards in the world.

That caution is clear in how radiation is treated. The plant is designed so that radiation exposure at its perimeter is lower than the dose from eating a single banana. Achieving this requires vast amounts of reinforced concrete in the reactor and containment structures, as radiation shielding relies on mass rather than technology.

Hinkley Point C follows established European reactor designs with strong safety records. The UK’s additional layers of protection reflect public and political caution rather than engineering necessity, reducing even theoretical risk to extremely low levels — but at a significant cost in carbon, materials, and construction effort.

While radiation risk is often the public focus — and is tightly controlled to levels lower than everyday exposure — the primary environmental concern at Hinkley is water. The power station requires a continuous intake of seawater from the Bristol Channel, around 132 cubic metres per second, to cool its reactors.

This presents two key risks to marine life:

• Impingement, where larger organisms are trapped against intake screens; and

• Entrainment, where smaller organisms are drawn through the cooling system and exposed to thermal shock, pressure changes, and mechanical damage.

Without mitigation, this process could affect millions of fish annually. Given that the Bristol Channel is both ecologically rich and legally protected, these risks became central to the planning process, driving intense scrutiny, public objection, and ultimately the requirement for an unusually robust suite of marine protection measures.

What is the “Fish Disco” — and how does it work?

The Fish Disco is the informal name for an acoustic fish deterrent system, designed to stop fish being drawn into the cooling-water intakes. The principle is straightforward: if an area is uncomfortable or confusing for fish, they will tend to avoid it.The system works as a series of layered defences, operating from the outside in.

1. Slow the water down - Low-velocity intake heads

The first and most important measure is passive. Seawater is drawn through long offshore tunnels that terminate in large intake heads designed to slow the water at the point of entry.

Fish are only pulled in if the flow exceeds their swimming ability. By reducing intake velocity, fish can sense the flow, turn, and swim away. The intake heads are also fitted with physical bars or screens to prevent larger animals entering at all. This is a built-in, low-tech solution that operates continuously without energy or intervention.

2. Warn fish before they get too close - The acoustic deterrent — “the Fish Disco”

Further out, the acoustic system comes into play. Fish rely heavily on sound for navigation and avoidance. Short, pulsed noises at certain frequencies trigger a natural avoidance response.

Arrays of underwater acoustic devices — essentially robust underwater speakers — emit these pulses when the plant is operating. The aim is not to blanket the seabed with noise, but to create a localised warning zone that most fish instinctively avoid.

The system has evolved during construction. Early designs relied on diver-installed equipment, which proved impractical in strong tidal conditions. The current approach uses high-frequency ceramic transducers that can be installed and serviced from the surface, improving safety and reliability. The underlying principle, however, remains unchanged.

3. Catch and return what slips through (Fish Recovery and Return system)

Even with slow intake flows and acoustic warning, some fish will still enter the system. Fine mesh screens inside the intake tunnels intercept fish before they reach the cooling equipment. Rotating brushes or water jets gently wash them into a separate channel, from which they are returned to sea via a dedicated outfall, away from the intake.

In simple terms: if a fish does get pulled in, the system tries to catch it alive and release it again. While similar systems exist elsewhere, the scale at Hinkley Point C is unusually large.

Why this matters & why it’s contentious

All of this takes place in the Severn Estuary and Bristol Channel, home to several migratory and protected species, including salmon, shad, lamprey, eel, and sea trout. With multiple environmental designations in place, inaction was never a realistic option.

That said, the numbers are uncomfortable. According to the developer’s own modelling, the expected annual benefit is small - around 0.08 salmon, 0.03 sea trout, 6 river lamprey, 18 Allis shad, and a few hundred Twaite shad, with newer estimates suggesting fewer than 100.

Set against a total fish protection programme costing over £700 million, critics question the value for money, with some estimating hundreds of thousands of pounds spent per fish saved.

From this perspective, the Fish Disco can appear as regulatory caution taken to its limits. But that is also what makes it revealing. It is not really about entertainment - and arguably not even just about fish — but about how major infrastructure is delivered in the UK, and how regulation, risk, public trust, and environmental law shape design decisions, sometimes regardless of cost efficiency.

Risk, green costs, and getting things built in the UK

The Fish Disco is not an anomaly. It reflects a wider shift in how large infrastructure projects are delivered in the UK, where environmental mitigation costs have escalated largely as a response to legal and consent risk rather than technical necessity alone.

A clear parallel can be seen in HS2’s bat mitigation works, where substantial sums have been spent on protecting bat flight paths and habitats along the rail corridor. As with Hinkley Point C, this is not a question of indifference to wildlife. The issue is structural: once a legally protected species is affected, the regulatory framework leaves little room for proportional judgement. The threshold is effectively binary. If a significant adverse effect is identified, the response must guarantee compliance, regardless of cost.

Where the risk now sits

Traditionally, the primary risks on major projects were engineering performance, safety, programme, and cost control. While those remain important, a significant share of project risk has shifted upstream into planning consent, regulatory challenge, and judicial review.

That shift has consequences. Faced with the prospect of lengthy delays or legal failure, developers are incentivised to over-mitigate rather than optimise. Measures such as the Fish Disco function less as finely tuned ecological interventions and more as insurance policies - designed to demonstrate unequivocal compliance, minimise challenge, and keep nationally significant projects moving. In that sense, the cost is not purely environmental. It is also the price of legal certainty.

The limits of cost–benefit analysis

This is where traditional cost–benefit analysis begins to break down. In theory, mitigation should be judged on whether the benefit achieved is proportionate to the cost. In practice, where protected species or designated sites are involved, the question becomes more basic: what is required to proceed lawfully at all? When compliance becomes binary — lawful or unlawful — economic optimisation is no longer the governing logic. Mitigation costs are set by the need to secure consent, not by the scale of the predicted impact.

The opportunity cost question

What often goes missing from public debate is opportunity cost. Hundreds of millions of pounds spent on highly localised mitigation are hundreds of millions not spent elsewhere — on housing delivery, energy affordability, broader environmental programmes, or the maintenance of existing infrastructure. This is not an argument against environmental protection, but a question of allocation and proportionality. A system that requires extreme expenditure to address marginal impacts risks constraining the wider public benefits that infrastructure is meant to deliver.

What this means for the built environment

For architects, engineers, planners, and developers, the implication is clear. Large projects today are shaped as much by regulatory defensibility as by design intent, technical performance, or human need. Environmental protection is no longer the question — that consensus is firmly established. The challenge is how to deliver it in a way that is proportionate, transparent, and compatible with the urgent need to build.

When good regulation starts to work against itself

It’s important to be clear: strong environmental regulation in the UK is well-intentioned and has delivered real gains. It exists because unregulated development has historically caused genuine harm, and few would argue for a return to that. The difficulty arises when layers of regulation accumulate to the point where the system begins to produce diminishing returns. In highly constrained contexts, additional mitigation does not always lead to proportionally better outcomes. Instead, it can:

• divert funding away from broader, more effective environmental programmes,

• slow or stall projects that deliver clear public benefit,

• and push decision-making towards defensibility rather than judgement

At that point, regulation can become self-defeating - protecting individual components of the environment in ways that undermine wider social and environmental goals.There is also a temporal issue. Delaying low-carbon energy or public transport infrastructure in pursuit of perfect mitigation can, in aggregate, cause greater environmental harm than the impacts being mitigated. In other words, the cost of delay is itself an environmental cost, but one that is rarely captured in formal assessments.

None of this suggests deregulation. Rather, it points to the need for:

• clearer proportionality tests,

• greater confidence in professional judgement,

• and a shift from project-by-project micromanagement towards strategic, landscape-scale environmental thinking.

The risk, otherwise, is that regulation designed to enable better outcomes ends up slowing the very transitions - decarbonisation, housing delivery, infrastructure renewal - that environmental policy ultimately exists to support.

Conclusion

The Fish Disco may sound whimsical, but it captures a serious reality of UK infrastructure delivery today. Major projects are increasingly shaped by regulation, legal risk, and the need to demonstrate absolute environmental compliance, often at very high cost.

This is not an argument against environmental protection. That principle is well established. The question is whether our current approach consistently delivers proportionate outcomes, or whether caution and legal defensibility are beginning to outweigh judgement.

For those of us in the built environment, the challenge is clear: we are designing not just infrastructure, but consentable systems. How well we balance environmental responsibility with human need will define what and how quickly we are able to build.

Works Cited

EDF Energy. Hinkley Point C: Marine Environment and Fish Protection Measures. EDF Energy, 2022.

Environment Agency. Cooling Water Intake and Fish Protection at Power Stations. UK Government, 2019.

European Commission. Nuclear Safety in the European Union. Publications Office of the European Union, 2020.

HM Government. National Policy Statement for Nuclear Power Generation (EN-6). Department for Energy Security and Net Zero, 2011.

International Atomic Energy Agency. Radiation Protection and Safety of Nuclear Power Plants. IAEA, 2018.

National Audit Office. Hinkley Point C. NAO, 2017.

Natural England. Severn Estuary Special Area of Conservation: Conservation Objectives. Natural England, 2021.

Office for Nuclear Regulation. Safety Assessment Principles for Nuclear Facilities. ONR, 2020.

Public Accounts Committee. HS2: Environmental Mitigation and Cost Control. UK Parliament, 2022.

Royal Society. Nuclear Power and the Environment. Royal Society Publishing, 2016.