Fish-Friendly Water Intake Screens: Meeting 316(b) and EU Regulations

Every year, conventional water intake structures kill billions of fish worldwide. A single UK power station, Longannet on the Forth estuary, impinged an estimated 56.6 million fish in just two years [1]. In Australia, unscreened irrigation diversions in the Murray-Darling Basin lose millions of Murray cod larvae in a single pumping season [2]. These are not rare catastrophes: they are the predictable, measurable outcome of poorly designed water intakes.

Regulators in the United States, European Union, United Kingdom, and Australia have responded with increasingly strict fish protection requirements for water intake structures. For engineers specifying intake screens, understanding these regulations is no longer optional: it is a mandatory prerequisite for permitting.

This guide turns the major fish protection regulations into practical engineering requirements, explains the two mechanisms that kill fish at intakes, and shows how Coanda screen technology achieves compliance through passive, inherently fish-safe design.

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Table of Contents

1. How Water Intakes Kill Fish: Impingement and Entrainment
2. Regulatory Framework: Four Jurisdictions, One Goal
3. Regulation Quick-Reference Table
4. Why Coanda Screens Are Inherently Fish-Friendly
5. Coanda Screen Slot Width Selection for Fish Protection
6. Coanda vs. Other Technologies for Fish Compliance
7. Case Evidence: Fish Passage Through Coanda Screens
8. Specifying a Fish-Compliant Coanda Screen
9. Frequently Asked Questions
10. References

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How Water Intakes Kill Fish: Impingement and Entrainment

Fish mortality at water intakes occurs through two distinct mechanisms. Understanding both is essential for selecting the right screening technology.

Impingement

Impingement occurs when fish are drawn against the surface of an intake screen by suction velocity and held there by the force of the water flow. Fish are unable to swim away from the screen face, leading to exhaustion, physical injury, suffocation, or death. Impingement disproportionately affects juvenile and weak-swimming fish that cannot generate enough thrust to escape the intake velocity field [1][3].

The critical variable is approach velocity: the speed of water perpendicular to the screen face. Higher approach velocities trap more fish and increase mortality. This is why every major fish protection regulation specifies a maximum intake velocity.

Entrainment

Entrainment occurs when organisms small enough to pass through screen openings (eggs, larvae, and fry) are drawn through the intake and into the downstream system (cooling circuit, penstock, treatment plant). Entrained organisms typically experience 100% mortality due to mechanical damage from pumps, turbines, pressure changes, temperature shock, and chemical exposure [3].

The critical variable is screen slot width (slot opening). If the slot is larger than the organism, the organism passes through and dies. This is why effective fish protection requires fine screening matched to the smallest life stage present at the intake site.

The key insight: Truly fish-friendly intake design must counter both impingement (through low approach velocity) and entrainment (through a narrow slot width). A technology that solves only one problem does not achieve compliance.

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Regulatory Framework: Four Jurisdictions, One Goal

United States: Clean Water Act Section 316(b)

Section 316(b) of the U.S. Clean Water Act requires that cooling water intake structures use the Best Technology Available (BTA) to minimize adverse environmental impact. The EPA's 2014 Final Rule [4] established national performance standards:

• Impingement mortality: No more than 24% mortality (including latent mortality) for all non-fragile species, measured using a sieve with maximum opening of 0.56 inches (14.2 mm) [4][5].
• Through-screen intake velocity: Maximum 0.5 fps (0.15 m/s) as a pre-approved compliance pathway [4].
• Entrainment: Site-specific studies required; the permitting authority (the EPA or state Director) determines BTA case by case [5].
• Applicability: Existing facilities withdrawing ≥2 million gallons/day from surface waters [4].
• Penalties: Civil penalties up to $60,000+ per day per violation. Criminal penalties possible for deliberate violations [6].

The 0.5 fps velocity standard was "pre-approved" by EPA, meaning facilities that meet it require no further impingement demonstration or monitoring: it is the simplest compliance pathway.

European Union: Water Framework Directive

The EU Water Framework Directive (WFD) [7] does not prescribe specific screen specifications. Instead, it requires all EU member states to achieve "good ecological status" for surface water bodies: which effectively mandates fish protection at any intake that could degrade fish populations.

Individual EU member states implement the WFD through national regulations that set screening requirements:

• Approach velocity: Typically 0.1–0.3 m/s depending on target species (juvenile salmonids: ≤0.12 m/s) [8].
• Slot widths: Species-dependent; salmon fry require 2–3 mm, juvenile fish 6–10 mm [8].
• Hydropower licensing: Fish screens are typically mandated as a condition of hydropower water abstraction (withdrawal) licences across the EU [8].

The WFD is currently under review, with expectations that fish protection requirements will tighten further in coming years.

United Kingdom: Environment Agency & Eels Regulations 2009

The UK has some of the most detailed fish screening regulations in the world, implemented by the Environment Agency (England), Natural Resources Wales, and SEPA (Scotland).

General fish screening guidance [9] sets maximum approach velocities perpendicular to the screen face ranging from 0.1 m/s to 0.75 m/s depending on target species:

Species / Life Stage	Max. Approach Velocity	Typical Mesh / Slot
Salmon / trout smolts	0.12 m/s	6–10 mm
Juvenile coarse fish	0.15 m/s	6–10 mm
Elvers (young eels)	0.10 m/s	1–2 mm
Adult eels	0.25 m/s	9–20 mm

Eels Regulations 2009 [10] are particularly stringent. Mesh size requirements vary by location:

Location	Required Maximum Mesh / Slot
Estuary to tidal limit	1 mm
Tidal limit to 30 km upstream	2–3 mm
30 km+ upstream of tidal limit	9–20 mm

Under the Eels Regulations, the Environment Agency can serve a formal notice on anyone who withdraws water, requiring them to screen intakes and outfalls for eel protection. Non-compliance is a criminal offense.

Australia: Murray-Darling Basin Fish Screening

Australia's fish screening guidelines, introduced in 2021, state [2][11]:

• Maximum approach velocity: 0.1 m/s (measured 80 mm in front of the screen face)
• Slot width: 2–3 mm (wedge wire)
• Velocity distribution: Must be spread evenly across the screen face to avoid hotspots
• Tolerance on gaps: Maximum 1–2 mm between moving parts

A major 2025 study on Murray cod larvae demonstrated that the 0.1 m/s + 2 mm combination achieved a 94% reduction in entrainment compared to unscreened conditions, with larvae being 63 times less likely to be entrained compared to 0.2 m/s conditions [2]. However, even modest departures from these standards (increasing velocity to 0.2 m/s or slot width to 3 mm) sharply increased mortality.

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Regulation Quick-Reference Table

Parameter	U.S. 316(b)	EU WFD (typical)	UK EA (general)	UK Eels Regs	Australia
Max. Approach Velocity	0.15 m/s (0.5 fps)	0.1–0.3 m/s	0.1–0.75 m/s (depends on species)	0.1 m/s (elvers)	0.1 m/s
Max. Slot / Mesh	14.2 mm (0.56 in) sieve	2–10 mm (depends on species)	1–20 mm (depends on species)	1–3 mm (depends on location)	2–3 mm
Mortality Standard	≤24% impingement	Good ecological status	Case-by-case	Criminal offense for non-compliance	Case-by-case
Applicability	≥2 MGD cooling water	All water withdrawals affecting ecological status	All regulated water withdrawals	Anyone who withdraws water, once served with a notice	Irrigation + all pump intakes

This table summarises published guidance as it stood when the article was written, and regulators revise both the criteria and their scope. Treat it as orientation: the values that apply to your project are the ones in the current regulation and in whatever the local agency writes into your withdrawal licence.

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Why Coanda Screens Are Inherently Fish-Friendly

Most intake screen technologies attempt to protect fish by reducing the harm caused by their fundamental operating mechanism: suction. Traveling screens add fish buckets. Drum screens add fish return troughs. Passive wedge wire screens rely on sweep velocity to carry fish past the screen before they are impinged.

Coanda screens take a fundamentally different approach: they eliminate the harm mechanism entirely.

1. No Suction: Zero Impingement Risk

A Coanda screen is a gravity-fed overflow device. Water flows over the weir and down the screen face under the force of gravity alone. There is no pump, no suction, and no intake velocity pulling water (and fish) toward the screen from the surrounding waterbody [12][13].

This means there is no impingement mechanism. Fish in the waterbody are never exposed to any flow that draws them toward the screen. Seen from the waterbody, the approach velocity is effectively zero.

2. Narrow Slot Exclusion: Zero Entrainment Risk

Coanda screens are manufactured with slot widths of 0.5 to 2.0 mm (1.0 mm standard), and narrower slots are available on request [12][13]. At 0.5 mm, even the smallest larval fish are physically excluded from passing through the screen. For comparison:

• Newly hatched Murray cod larvae measure approximately 13.2 mm long × 2.1 mm wide [2]: excluded by 2 mm slots
• Salmon fry are typically >25 mm: excluded by all standard Coanda slot widths
• Elvers (glass eels) are approximately 6–8 mm diameter: excluded by slots ≤5 mm

With a 1.0 mm slot Coanda screen, entrainment of any vertebrate organism is physically impossible.

3. Surface-Mounted Design: No Underwater Entrapment

Because Coanda screens are mounted on top of a weir, above the waterline, fish in the river or creek are never in contact with the screen surface during normal conditions. Fish approach the weir, sense the increasing velocity, and move away. Any fish that does pass over the weir is swept across the screen face and returned to the watercourse via the bypass channel, undamaged.

4. Continuous Self-Cleaning: Clogging Does Not Raise Impingement Risk

When conventional screens clog with debris, the effective open area decreases and through-screen velocity rises sharply in the remaining open slots: dramatically increasing impingement risk. Coanda screens are continuously self-cleaning through hydraulic action, maintaining uniform velocity distribution across the entire screen face at all times [12].

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Coanda Screen Slot Width Selection for Fish Protection

Selecting the correct slot width requires matching the slot width to the smallest fish life stage present at the intake site during the operating season.

Target Species / Life Stage	Minimum Body Width	Recommended Max. Slot Width	Regulatory Basis
All larval fish (generic)	1–3 mm	1.0 mm	Conservative: excludes all larvae
Murray cod larvae	~2.1 mm	2.0 mm	Australian guidelines [2]
Salmon fry	~4–6 mm	3.0 mm	WDFW / NOAA guidelines [14]
Elvers (glass eels)	~6–8 mm	1.0 mm (UK estuarine)	UK Eels Regulations [10]
Juvenile salmonids	~10–15 mm	6.0 mm	EU WFD typical [8]
Adult eels	~20–40 mm	9–20 mm	UK EA upstream [10]

ADENCO recommendation: For sites where multiple species and life stages are present, choose 1.0 mm slots, the level most regulations require; where larval fish must be excluded, choose 0.5 mm. This covers most species and seasons and reduces the risk of regulatory changes requiring a retrofit.

On shallow screen slopes capacity falls as the slot narrows, so a narrower slot means more screen width for the same flow [12]: choosing 1.0 mm instead of 1.5 mm is allowed for when the screen is sized.

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Coanda vs. Other Technologies for Fish Compliance

Compliance Factor	Coanda Screen	Traveling Screen (316b)	Drum Screen	Passive Wedge Wire
Impingement mechanism	None (gravity-fed)	Suction (reduced by fish buckets)	Suction (reduced by return trough)	Suction / sweep velocity
Entrainment prevention	Physical exclusion (0.5 to 2.0 mm slots, 1.0 mm standard; narrower on request)	Fish buckets (larger organisms only)	Mesh exclusion (0.2–3 mm)	Physical exclusion (1–10 mm)
Larval protection	Excellent (≤1 mm slot)	Poor (larvae pass through)	Good (fine mesh available)	Good (narrow slot available)
Electricity required	None	Yes (motor + spray)	Yes (motor + spray)	None (or airburst)
Fish handling mortality	N/A (no fish contact)	<5% (modified Ristroph) [15]	Variable	N/A (no fish contact)
Biofouling risk	Low (surface-mounted, self-cleaning)	Low (continuous motion)	Low (continuous motion)	High (submerged, static)
Regulatory acceptance	High (proven fish-safe)	High (316b standard)	Medium (site-specific)	High (proven fish-safe)

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Case Evidence: Fish Passage Through Coanda Screens

Salmon Smolt and Fry

Research by Buell (2000) at Coanda screen sites confirmed that both salmon smolt and fry can pass over Coanda screens undamaged [16]. Fish that approach the weir are swept across the screen face by the flow and discharged into the bypass channel without injury. The screen does not trap, hold, or impinge fish at any point.

FIThydro Project (EU Horizon 2020)

The EU's FIThydro research project (2017–2021), involving 26 partners across 10 countries, evaluated fish-friendly technologies for hydropower including Coanda-type intakes [17]. The project confirmed that bottom-type Coanda intakes can function as effective fish barriers while maintaining water diversion, provided that:

• Adequate flow is maintained across the entire screen to prevent fish from being stranded on the screen
• Sufficient water depth below the screen (a plunge pool) is provided so that fish are not injured when they fall from the screen
• Slot openings are matched to target species

2026 Systematic Review of Fish Guidance Barriers

A comprehensive 2026 systematic review of 96 studies on fish guidance barriers [18] found that physical screens remain among the most effective fish protection technologies. The review reported that multimodal systems (combining physical barriers with behavioral deterrents) achieve approximately 80% guidance efficiency, while physical screens alone can achieve even higher exclusion rates when properly designed for the target species.

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Specifying a Fish-Compliant Coanda Screen

When specifying a Coanda screen for a project with fish protection requirements, include these parameters in your specification:

1. Target species and life stages: List all species present at the intake site, including seasonal migrants (eels, salmon). Identify the smallest life stage that may be present during the operating season.

2. Applicable regulations: State which regulatory framework(s) apply: Section 316(b), EU WFD national implementation, UK EA guidance, Eels Regulations, Australian guidelines, or state/provincial requirements.

3. Maximum slot width: Based on the smallest organism to be excluded. State the maximum allowable slot width in millimetres.

4. Design flow and available head: Required to size the screen. ADENCO uses the US Bureau of Reclamation (USBR) Coanda Design Guide (Wahl, 2003, report R-2003-03) [12] to calculate the optimal screen dimensions for the specified slot width and flow.

5. Environmental conditions: Water temperature range, sediment load, ice risk, and debris type. These affect material selection and any anti-icing treatment requirements.

6. Monitoring and reporting requirements: Some permits require ongoing monitoring of fish impact. Coanda screens simplify this because the bypass channel provides a natural monitoring point for any organisms that pass over the screen.

Request a fish-compliant Coanda screen quote: ADENCO's engineering team will review your regulatory requirements and provide a screen specification that can be supplied to meet the applicable compliance thresholds.

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Frequently Asked Questions

Do Coanda screens meet Section 316(b) requirements?

Yes. Coanda screens exceed 316(b) requirements through fundamentally different design. Because they are gravity-fed with no suction, the approach velocity from the waterbody is effectively zero: far below the 0.5 fps (0.15 m/s) threshold. Slot widths of 0.5–1.0 mm physically exclude organisms much smaller than the 0.56-inch sieve standard. And with no impingement mechanism, mortality is zero rather than the 24% maximum allowed.

What slot size do I need for fish protection?

The required slot size depends on the species and life stages present at your intake. For the fish protection level most regulations require, choose 1.0 mm slots; where larval fish must be excluded, choose 0.5 mm. For sites where only juvenile and adult fish are present, 2–3 mm slots are typically sufficient. UK estuarine sites subject to Eels Regulations require 1 mm slots. Contact ADENCO with your site details for a species-specific recommendation.

Are Coanda screens approved for use in the EU?

Yes. Coanda screens are widely installed at European hydropower sites, with over 40 installed screens, mainly in the Alps and the UK [19]. They can be supplied to meet EU Water Framework Directive requirements for maintaining good ecological status, because they provide effective fish exclusion without impingement, entrainment, or habitat disruption.

Can a Coanda screen protect larval fish?

Yes. A Coanda screen with 1.0 mm slots physically excludes all larval fish. Research on Murray cod larvae (among the smallest at ~2.1 mm body width) demonstrated that 2 mm wedge wire screens at 0.1 m/s approach velocity achieve 94% entrainment reduction [2]. At 1.0 mm slots, entrainment of any larval fish is physically impossible.

What is the penalty for non-compliance with fish screening regulations?

In the United States, Section 316(b) violations can result in civil penalties of over $60,000 per day per violation, plus criminal penalties for deliberate violations [6]. In the UK, failure to comply with Eels Regulations or Environment Agency screening notices is a criminal offense. EU member states impose penalties under their national WFD implementation laws. The financial risk of non-compliance far exceeds the cost of proper screening.

Do I need a fish screen for an irrigation intake?

In many jurisdictions, yes. Australia requires fish screening at all pump-operated irrigation intakes in the Murray-Darling Basin. In the UK, the Eels Regulations can require screening at any water withdrawal point. In the U.S., state-level requirements vary but are expanding. Even where not currently mandated, installing a fish-protective screen now avoids costly retrofit when regulations tighten: as they have in every major jurisdiction over the past decade.

How does a Coanda screen compare to a traveling screen for fish protection?

Both can achieve regulatory compliance, but through different mechanisms. A traveling screen reduces impingement by collecting fish in buckets and returning them to the water, achieving <5% handling mortality under the best conditions. A Coanda screen eliminates impingement entirely because there is no suction: fish never contact the screen. For entrainment, Coanda screens physically exclude organisms through narrow slots (≤1 mm), while traveling screens allow small organisms to pass through and are ineffective for larval protection.

Do Coanda screens work for eel protection?

Yes. For UK sites subject to the Eels Regulations 2009, Coanda screens can be supplied with 1.0 mm slots to meet the most stringent estuarine requirement. The passive, gravity-fed operation means there is no suction to attract eels toward the intake, and the narrow slot physically excludes even glass eels (elvers). The slot width matches the 1 mm mesh the regulation requires at estuarine sites; the absence of suction adds protection beyond what the regulation asks for.

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References

1. Turnpenny, A.W.H. et al. (2008). "Fish mortality by impingement on the cooling-water intake screens of Britain's largest direct-cooled power station." Marine Pollution Bulletin, 56(4), pp. 723–739.

2. Baumgartner, L. et al. (2025). "Protecting Larval Fish at Water Intakes: Hydraulic and Biological Evidence for the Effectiveness of Modern Fish-Protection Screens." Biology Open, Vol. 14, No. 12. PMC12755069.

3. NOAA. "Fish Entrainment and Impingement Studies." National Marine Fisheries Service. Retrieved April 2026, from https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/mfr39102.pdf

4. U.S. EPA. (2014). "National Pollutant Discharge Elimination System: Final Regulations to Establish Requirements for Cooling Water Intake Structures at Existing Facilities." Federal Register, 79 FR 48300. https://www.federalregister.gov/documents/2014/08/15/2014-12164/

5. 40 CFR Part 125, Subpart J: Requirements Applicable to Cooling Water Intake Structures for Existing Facilities Under Section 316(b) of the Clean Water Act. https://www.ecfr.gov/current/title-40/chapter-I/subchapter-D/part-125/subpart-J

6. "Section 316(b): Compliance, Penalties, and Exemptions." LegalClarity. Retrieved April 2026, from https://legalclarity.org/section-316b-compliance-penalties-and-exemptions/

7. EU Water Framework Directive. European Commission. Retrieved April 2026, from https://environment.ec.europa.eu/topics/water/water-framework-directive_en

8. "Fish Screens in Hydropower Plants." Waterman Australia. Retrieved April 2026, from https://watermanaustralia.com/fish-screens-in-hydropower-plants/

9. UK Environment Agency. "Screening for Intake and Outfalls: A Best Practice Guide." https://assets.publishing.service.gov.uk/media/5a7c9293ed915d6969f45d2d/scho0205bioc-e-e.pdf

10. UK Environment Agency. "Screening at Intakes and Outfalls: Measures to Protect Eel." https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1097095/Withdrawn-Screening-at-intakes-and-outfalls-measures-to-protect-eel.pdf

11. "Murray Cod and Modern Fish Screens: Influence of Water Velocity and Screen Design." Marine & Freshwater Research, Vol. 75, No. 4 (2024). https://www.publish.csiro.au/MF/MF23239

12. Wahl, T.L. (2003). Design Guidance for Coanda-Effect Screens. U.S. Bureau of Reclamation, Research Report R-2003-03. Denver, CO.

13. Wahl, T.L. (2001). "Hydraulic Performance of Coanda-Effect Screens." Journal of Hydraulic Engineering, Vol. 127, No. 6, pp. 480–488. ASCE.

14. Washington Department of Fish and Wildlife. "Fish Protection Screen Guidelines." https://wdfw.wa.gov/sites/default/files/publications/00050/wdfw00050.pdf

15. "EPA 316(b) Compliant Fish Screens." Atlas-SSI. Retrieved April 2026, from https://www.atlas-ssi.com/intake-screens/traveling-water-screens/316b-fish-handling/

16. "Bottom-type intakes (Coanda screen, Lepine water intake, etc)." FIThydro Wiki, EU Horizon 2020. https://www.fithydro.wiki/index.php/Bottom-type_intakes_(Coanda_screen,_Lepine_water_intake,_etc)

17. FIThydro: Fish-Friendly Innovative Technologies for Hydropower. EU H2020 Project No. 727830. https://cordis.europa.eu/project/id/727830

18. Meister, J. et al. (2026). "Barriers for Fish Guidance: A Systematic Review." MDPI Water, Vol. 18, No. 2, 225.

19. "The Coanda Effect." International Water Power & Dam Construction. Retrieved April 2026, from https://www.waterpowermagazine.com/analysis/the-coanda-effect/

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Published by ADENCO: Advanced Engineering Coanda Intake Screens. ADENCO provides Coanda intake screens that can be supplied to meet Section 316(b), EU Water Framework Directive, UK Environment Agency, and Australian fish screening requirements. Contact our engineering team to discuss your regulatory requirements and receive a project-specific specification.