A fish screen is designed to prevent

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

from swimming or being drawn into an aqueduct, cooling water intake,

intake tower An intake tower or outlet tower is a vertical tubular structure with one or more openings used for capturing water from reservoirs and conveying it further to a hydroelectric or water-treatment plant. Unlike spillways, intake towers are intended ...

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

or other diversion on a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

or waterway where water is taken for human use. They are intended to supply debris-free water without harming aquatic life. Fish screens are typically installed to protect

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

of fishes that would otherwise be harmed or killed when passing through industrial facilities such as steam electric power plants,

hydroelectric Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...

generator Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...

petroleum refineries An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefie ...

chemical plant A chemical plant is an industrial process plant that manufactures (or otherwise processes) chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transform ...

s, farm

irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...

water and municipal drinking water treatment plants. However, many fish are killed or injured on screens or elsewhere in the intake structures.

Design

Industrial facilities

Fish screens may be positive barriers (devices such as a perforated metal plate that physically prevents fish from passing) or behavioral barriers (devices that encourage fish to swim away). Most behavioral barriers are experimental and of unproven effectiveness. Cooling water intake & travelling screens

Cooling water intake & travelling screens

Positive barriers are often effective at keeping aquatic organisms from entering a cooling system, but may also kill them by impinging them on the screens. These barrier types are widely used and include: * Modified traveling screens * Fish handling and return systems * Horizontal, flat-plate screens with bypass water return systems * Cylindrical wedgewire screens * Fine-mesh screens * Fish net barriers. Besides simply preventing fish from passing, fish screens are designed to minimize stress and injury that occur when fish impact the screen or are subjected to changes in water velocity and direction caused by the diversion. The U.S.

Environmental Protection Agency A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...

(EPA) has evaluated other barrier technologies and identified some as potentially effective, although not widely demonstrated (as of 2004): * Aquatic microfiltration barriers * Angled and modular inclined screens * Velocity caps. Some fish screens are designed to protect a single species of fish (for example,

salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...

) and are not necessarily effective at protecting other fish species. Some screens are capable of protecting more than one species or type of life. Additionally, some screens may effectively protect juvenile and adult fish, but not fish eggs and

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e.EPA (2002). "National Pollutant Discharge Elimination System—Proposed Regulations to Establish Requirements for Cooling Water Intake Structures at Phase II Existing Facilities; Proposed Rule." . 2002-04-09. The cost of a fish screen varies from thousands of US dollars for small, low-flow-rate screens to millions of US dollars in the case of very large custom-designed systems that filter a large flow of water. Maintenance costs can be significant, including repairs, removing trash, and adjusting the equipment for changes in stream conditions.

Non-industrial applications

For some low volume, non-industrial water diversion applications, there are screens available that have no moving parts, do not require electricity, and have very little need for maintenance.

Impacts on aquatic life

Many power plants and other industries in the U.S. continue to use screens that impinge fish. For example, the cooling system at the

Indian Point Energy Center Indian Point Energy Center (I.P.E.C.) is a three-unit nuclear power plant station located in Buchanan, just south of Peekskill, in Westchester County, New York. It sits on the east bank of the Hudson River, about north of Midtown Manhattan. Th ...

in New York kills over a billion fish eggs and larvae annually. At the Bay Shore Power Plant in

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

, 46 million fish were killed over an 18-month period. Organisms that pass through the screens are killed or stressed (depending on the species) as they become entrained in the cooling system. 208 million fish eggs and over 2 billion small and larval fish were entrained at the Bay Shore plant over the same 18 months. EPA estimates that billions of fish and other organisms are killed each year in cooling water intakes.

Legal requirements

In the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, the

National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the stew ...

, a division of

NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

, mandates positive-barrier fishscreens in most new diversions from waterways where endangered or threatened fish species occur. Some existing unscreened diversions whose construction pre-dates fish-screen mandates are allowed to continue operating by

grandfather rule The grandfather rule, in sports which usually only permit participants to play for the team of their country of birth, is an exception which gives participants the option to play for the country of any of their ancestors up to the grandparents. ...

. The U.S.

Clean Water Act The Clean Water Act (CWA) is the primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters; recognizing the responsibiliti ...

requires EPA to issue

regulation Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. For ...

s on industrial cooling water intake structures. The agency issued regulations for new facilities in 2001 (amended 2003), and for existing facilities in 2014.EPA
"National Pollutant Discharge Elimination System—Final Regulations To Establish Requirements for Cooling Water Intake Structures at Existing Facilities and Amend Requirements at Phase I Facilities"
Final rule. ''Federal Register,'' 79 FR 48300. 2014-08-15.

References

External links

Cooling Water Intakes
- U.S. EPA regulatory program
Install Time Lapse
- Time lapse video of a small fish conservation screen being installed {{fishery science topics, expanded=science Aquatic ecology Fish conservation