United States Department of Agriculture 396-CPS-1

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NRCS reviews and periodically updates conservation practice standards. To obtain the current 

version of this standard, contact your Natural Resources Conservation Service State office or 

visit the Field Office Technical Guide online by going to the NRCS website at 

https://www.nrcs.usda.gov/ and type FOTG in the search field. 

USDA is an equal opportunity provider, employer, and lender.

Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

AQUATIC ORGANISM PASSAGE 

CODE 396 

(mi)

DEFINITION 

Modification or removal of barriers that restrict or impede movement of aquatic organisms. 

PURPOSE 

This practice is used to accomplish the following purpose: 

• Provide access to habitat by improving or providing passage for aquatic organisms. 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies to all aquatic habitats where barriers impede passage of aquatic organisms. Barriers

could include physical barriers, temperature or water quality/quantity, velocity, or turbulence. 

CRITERIA 

General Criteria Applicable to All Purposes 

Planning and evaluation 

Evaluate the existing channel stability and geometry when determining the type of structure to be

installed. 

Evaluate sites for variations in stage and discharge, tidal influence, hydraulics, geomorphic impacts,

sediment transport and continuity, and organic debris movement. Design passage structures to account

for the known range of variation resulting from this evaluation. 

Mitigate undesirable channel profile shifts resulting from the modification or removal of a passage barrier.

Examples of channel plan or profile shifts could include head cuts resulting from barrier removal or silt

accumulation above existing barriers depositing downstream. Analyze the removal of obstructions using

appropriate stream and geomorphic procedures. 

Plan and locate passage for compatibility with local site conditions and stream geomorphology, to the

extent possible. 

Evaluate existing roads that have created barriers to determine whether it is appropriate to replace or to

remove existing stream crossings. Road realignment to avoid stream crossings must be included in this

evaluation. 

Evaluate the effects of planned works on public safety and flooding. 

Barrier removal, upgrades, or retrofitting can significantly affect wetlands, flooding potential, existing

infrastructure, and social and cultural practices and resources. Evaluate and consider the full range of

impacts when planning or designing projects. 
If passage was not historically present, an evaluation must be conducted to document that native species

above the barrier will not be negatively impacted. 

Design requirements 

When possible, use design solutions that simulate the characteristics of adjacent natural channel

geometry and morphology. 

Evaluate the type and size of woody material, sediment, and debris upstream of the structure and how the

passage structure will allow it to pass downstream. 

If using the hydraulic design method, design passage structures according to known size, shape,

swimming, and leaping capabilities of target species or a similar species with comparable swimming

abilities to accommodate the movement and migration requirements throughout their life cycle. 

Determination of the high and low fish passage design flows, water velocity and water depth is also

required for the hydraulic design method. 

Document how designs satisfy the physiological requirements of target organisms. 

Design passage to accommodate present and reasonably anticipated changes in watershed conditions. 

At a minimum, design and evaluate passage structures for hydraulic performance and structural integrity

at the bankfull and 25-year peak flow. 

For structural design elements such as side slope requirements, stream approaches, load capacity, etc.,

reference requirements outlined in the NRCS National Engineering Manual (NEM) (Title 210), Part 536,

“Structural Engineering,” the NRCS National Engineering Handbook (NEH) (Title 210), Part 654, “Stream

Restoration Design,” and appropriate engineering practice standards. 

Use trashracks only if required or necessary. Ensure that trashracks are either self-cleaning or easily

maintained. 

Select construction materials that are nontoxic and resistant to degradation. 

Prior to construction, develop a written plan to address bypass flows during construction that contains

guidance on pumping or rerouting of flows, aquatic species removal, pollution control, and project

scheduling. The plan can be developed by NRCS and the contractor or by an outside party, but it must

meet all NRCS and permit requirements. 

Plan construction logistics, methods, and sequencing to minimize adverse effects to aquatic organisms,

riparian areas, and instream habitat. 

Take measures to prevent invasive species introductions during construction activities, including

inspecting all vehicles prior to entering the site. 

Use weed-free certified mulch when revegetating disturbed areas. 

Additional Criteria Applicable to Stream Crossings 

In streams with anadromous salmonid species, designs for bridges, bottomless arches, and culverts must

have a streambed width and channel slope that is determined according to the National Marine Fisheries

Service (NMFS) publication “Anadromous Salmonid Passage Facility Design.” Non-anadromous streams

and streams with resident species should, at a minimum, meet guidelines identified by State agencies

responsible for fish resources. 

If ice jams or woody debris passages are a concern, increase the span and/or allow for extra clearance

between the channel bottom and bridge low chord or top of culvert. 

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Additional Criteria Applicable to Fish Ladders 

Conduct an assessment of structural integrity and stability when passage structures are to be integrated

with an existing structure. 

Avoid locating fishway entrances and exits in areas that will obstruct function, increase harassment or

predation, or result in excessive operation and maintenance requirements. 

Allow sufficient space between fishways exits and spillways, intakes, or other hydraulic structures to not

harm target species. 

Provide adequate attraction flow into a passage facility across the full range of discharge during which

target species will move. See guidance in NRCS 210-NEH-654, Technical Supplement 14N, “Fish

Passage and Screen Design.” 

Additional Criteria Applicable to Instream Channel Bed Modifications and Nature-like Fishways 

New streambed materials should be composed of materials of similar composition (size, shape, and

distribution) to natural streambed materials that form the natural stream channels. There should be a

minimum of 5 percent to a maximum of 10 percent fines in the new streambed materials to prevent a

porous bed. 

Designs for road abandonment and culvert removal must include a new channel segment through the

existing road fill prism that meets or exceeds the requirements for streambed width and channel slope to

provide passage for aquatic organisms based on the stream simulation design method. See NRCS

Conservation Practice Standard (CPS) Open Channel (Code 582) and Channel Bed Stabilization (Code

584). 

Additional Criteria Applicable to Fish Screens 

Screens implemented under this practice are for the purpose of protecting species movement within the

natural stream channel and will prevent species from accessing irrigation canals, farm fields, or other

nonaquatic environments. 

Locate screens based on minimizing the delay of fish encountering the diversion. 

Ice and debris loads must be considered when designing screen structures. 

Target species size and swim capabilities will determine screen mesh size requirements. Many species

can be protected utilizing NMFS juvenile salmonids requirements (Nordlund, 2008); however, locations

with non-salmonid species should also use local and State guidelines. See guidance in NRCS 210-NEH654, Technical Supplement 14N, “Fish Passage and Screen Design.” 

CONSIDERATIONS 

Develop or adopt a quantitative method to identify and evaluate passage barriers (see “References”). 

Remove passage barriers rather than installing or retrofitting a new facility or structure. Complete or partial

barrier removal often provides better passage conditions and is more economical than designing,

constructing, operating, and maintaining many new passage structures. 

Bridges, culverts, or bottomless arches designed using the stream simulation approach (USDA Forest

Service, 2008) that incorporate natural streambed substrates throughout their length are preferred over

other culvert configurations for passage purposes. 

Bridges are the preferred structure type when the bankfull width is greater than 20 feet. Bankfull widths

less than 20 feet may use a bridge, bottomless arch, or embedded culvert. 

Design and locate features to improve or provide passage for as many different aquatic and semi-aquatic

species and age classes as possible. 

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Retain as much riparian and streambank vegetation as possible during project access and construction

activities to maintain shade, riparian continuity, and sources of nutrient and structural inputs for aquatic

ecosystems. 

Restore temporary construction areas using native vegetation appropriate to the site and consider

opportunities to enhance wildlife and pollinator habitat. 

Where appropriate, remove access roads or trails and restore native vegetation representative of the site. 

Replacing or removing an existing instream structure may trigger channel adjustments (e.g., aggradation

and/or degradation) upstream and/or downstream of the work site. Restore natural stream grade at the

site if possible and when appropriate, constructed riffle/roughened channel design solutions are preferred

over channel spanning grade control structures. To mitigate adverse physical or ecological consequences

of existing structure removal see NRCS CPSs Channel Bed Stabilization (Code 584) and Grade

Stabilization Structure (Code 410). 

Analyze any potentially negative interactions (including hybridization, disease, competition, or predation)

between target and aquatic nuisance species when passage is provided above a barrier. If serious

consequences are likely, take steps to minimize adverse effects. 

Incorporate the habitat requirements of other aquatic, semi-aquatic, or terrestrial species that may be

affected by a passage project. Some passage facilities may improve survival for terrestrial vertebrates by

providing safe migration routes under roadways by providing a bankfull or floodplain bench through the

structure or through the use of additional floodplain relief culverts. 

Assess the amount of habitat upstream and downstream of a barrier to evaluate for project feasibility, cost

effectiveness, and/or potential for connecting fragmented habitats. Using a watershed approach whenever

possible provides a framework for project planning. 

Fish passage facilities are often associated with water diversions or intakes that may injure or kill aquatic

species. Prevent fish entrainment or impingement, particularly of juveniles, into diversions, penstocks, or

pumps by installing screens. 

Passage projects can affect water management practices such as diversion, power generation, or storage.

Strive to balance aquatic organism passage with other water management objectives. 

Consider upstream and larger watershed issues that may affect passage. Common solutions may include

maintaining or restoring adequate instream flow and/or other water quality parameters (e.g., temperature,

dissolved oxygen). 

Floodplain and water development often alter historic river channel pattern and location. Consider

bypassing a barrier by restoring streamflow to former, stable natural channels. 

Passage facilities can assist population recovery and management. Consider local, State, or Federal

brood stock collection and management of nonnative species when planning passage features. 

Consider using self-regulating tidegates in marine environments. These structures can be adjusted to

automatically regulate saltwater intrusion into estuaries and often improve estuarine functions and

passage conditions. 

Water quality impacts from vehicular pollutants and erosion caused by tire action can be severe. Where

possible, reroute roadways or install hardened instream crossings (see NRCS CPS Stream Crossing

(Code 578)). Also consider placing crushed aggregate at crossing approaches, running planks on the full

width of timber bridges, design road ditch turnouts away from the stream, and construct waterbars to

reduce direct input of sediment into the stream. 

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PLANS AND SPECIFICATIONS 

Provide site-specific plans for this practice. Plans and design documents will specify passage structure

design, layout, and overall goals and objectives, and include (at a minimum)— 

• Location map and plan view of site, and description of design flows. 

• Identification of the species of interest and specific passage requirements. 

• A project map or description that includes known and/or potential upstream or downstream barriers

affecting the project goals. This will include documentation of miles of access to the next passage

barrier for reporting purposes as outlined in the NRCS National Biology Handbook (Title 190),

Subpart D, Part 640.00, “Guidance for Assessing and Reporting Stream Miles Affected by Activities

Completed Under Conservation Practice Standard 396, Fish Passage.” 

• Detailed construction drawings showing existing and planned site conditions including elevations,

typical profiles, and cross sections of planned structures. 

• Construction specifications describing materials, logistics (including erosion control), and timing. 

OPERATION AND MAINTENANCE 

Develop an operation and maintenance plan for all applications of this standard. Within the plan, provide

for periodic inspection and corrective action should passage conditions become impaired because a

structure is damaged or inoperable. At a minimum, operation and maintenance items should include— 

• Guidance for post-construction evaluation and monitoring to assess structural integrity and

compliance with design criteria. 

• Specifying what entity is responsible for the daily operation and maintenance of a passage

structure. 

• Annual, seasonal, and/or daily operating activities necessary to ensure proper function of the

structure. 

• Checking passage structure at regular intervals to ensure it is operating within design criteria. 

• Cleaning trashracks, fish screens, and debris collectors or removing debris accumulations regularly. 

• Adjusting gates, orifices, valves, or other control devices as needed to regulate flow and maintain a

passage structure within operating criteria. 

• Periodically checking flow metering devices for accuracy. 

• Annually inspecting passage structures for structural integrity and disrepair. 

• Inspecting gate and valve seals for damage. 

• Replacing worn or broken stoplogs, baffles, fins, or other structural components. 

REFERENCES 

Aquatic Nuisance Species Task Force. 2011. “Aquatic Nuisance Species.” Accessed March 22, 2021.

https://www.anstaskforce.gov/ans.php

Barnard, R. J., J. Johnson, P. Brooks, K. M. Bates, B. Heiner, J. P. Klavas, D.C. Ponder, P.D. Smith, and P.

D. Powers. 2013. Water Crossings Design Guidelines, Washington Department of Fish and Wildlife,

Olympia, Washington. https://wdfw.wa.gov/sites/default/files/publications/01501/wdfw01501.pdf

Mefford, B. 2014. Pocket Guide to Screening Small Water Diversions. U.S. Bureau of Reclamation,

Denver Technical Service Center. 

https://www.usbr.gov/tsc/techreferences/hydraulics_lab/pubs/manuals/Small%20Screen%20Design%20M

anual%20USBR.pdf

National Marine Fisheries Service. 2022. NOAA Fisheries West Coast Region Anadromous Salmonid

Passage Design Manual, NMFS, WCR, Portland, Oregon. https://media.fisheries.noaa.gov/2022-

08/anadromous-salmonid-passage-design-manual-2022.pdf 

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Nordlund, B. 2008. Designing Fish Screens for Fish Protection at Water Diversions. National Marine

Fisheries Service. https://www.fishscreensoc.com/wp-content/uploads/2016/10/DESIGNING-FISHSCREENS-2008.pdf 

Turek, J., A. Haro, and B. Towler. 2016. Federal Interagency Nature-like Fishway Passage Design

Guidelines for Atlantic Coast Diadromous Fishes. Interagency Technical Memorandum.

https://www.fws.gov/northeast/fisheries/pdf/NMFS_2016_Federal_Interagency_NLF_Passage_Design_Gu

idelines.pdf

USDA Forest Service. 2006. Low-Water Crossings: Geomorphic, Biological, and Engineering Design

Considerations. 0625 1808—SDTDC. San Dimas, CA.

https://www.fs.fed.us/eng/pubs/pdf/LowWaterCrossings/LoWholeDoc.pdf

USDA Forest Service. 2008. Stream Simulation: An Ecological Approach to Providing Passage for Aquatic

Organisms at Road-Stream Crossings. 0877 1801—SDTDC. San Dimas, CA.

https://www.fs.fed.us/eng/pubs/pdf/StreamSimulation/hi_res/%20FullDoc.pdf

USDA NRCS. 2008. National Engineering Handbook (Title 210), Part 654, Stream Restoration Design.

Washington, D.C. https://directives.sc.egov.usda.gov/. 

USDA NRCS. 2009. National Biology Handbook, Subpart B, Conservation Planning. Washington, D.C.

https://directives.sc.egov.usda.gov/

USDA NRCS. 2010. National Engineering Manual (Title 210), Part 536, Structural Engineering.

Washington, D.C. https://directives.sc.egov.usda.gov/. 

USDA NRCS. 2012. National Engineering Handbook (Title 210), Part 630, Hydrology. Washington, D.C.

https://directives.sc.egov.usda.gov/. 

USDA NRCS. 2013. National Engineering Manual (Title 210), Part 531, Geology. Washington, D.C.

https://directives.sc.egov.usda.gov/. 

USDA NRCS. 2021. National Engineering Handbook (Title 210), Part 650, Chapter 16, Soil

Bioengineering for Streambank and Shoreline Protection. Washington, D.C.

https://directives.sc.egov.usda.gov/. 

USDI Bureau of Reclamation. 2008. Fish Passage for Non-Salmonids. Western Water and Power Solution

Bulletin. https://www.usbr.gov/research/projects/download_product.cfm?id=2180

U.S. Fish and Wildlife Service. 2017. Fish Passage Engineering Design Criteria. USFWS, Northeast

Region R5, Hadley, Massachusetts.

https://www.fws.gov/northeast/fisheries/pdf/USFWS_R5_2017_Fish_Passage_Engineering_Design_Criter

ia.pdf

U.S. Fish and Wildlife Service. 2022. Culvert Design Guidelines for Ecological Function.

https://www.fws.gov/alaska-culvert-design-guidelines

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