National Inventory of Dams

The National Inventory of Dams (NID) is the central repository for information about dams in the U.S. and its territories that meet specific criteria. The congressionally authorized database shows the location of these dams and serves as a resource to support awareness and preparedness for a dam-related emergency. USACE is responsible for maintaining the NID and closely collaborates with federal and state dam regulating agencies to obtain accurate and complete information about dams in the database. More information is available in the NID Overview fact sheet and by visiting

Click here to access NID information for Raystown. 

Questions or Comments?

For more info regarding the risks associated with living near Raystown Lake, contact our Public Affairs Office at

Raystown Lake Overview

The U.S. Army Corps of Engineers (USACE) built Raystown Dam in 1972 to reduce the risk of flooding to downstream communities by storing water during major flood events.  The dam is located on the Raystown Branch Juniata River, approximately 5.5 miles upstream of the confluence with the Juniata River.  The dam is located in Huntingdon and Bedford Counties, approximately 3.5 miles south of the Borough of Huntingdon, PA.  The dam consists of an earthen embankment, behind which Raystown Lake is impounded. The primary purpose for Raystown Dam is for flood risk management to reduce downstream river levels during flood events. In addition, the water stored in the reservoir and the releases from the dam also provide additional benefits for water quality, hydropower and recreation during non-flood periods. Releases from the dam can be made through the hydropower plant, a gated spillway, and a gated conduit.  The project also includes an ungated spillway which can release large flows during extreme flood events.  A small earthen embankment named Hesston Dike is also associated with Raystown Dam and is located near the town of Hesston, PA.  This dike is listed separately within the National Inventory of Dams and, during large floods, blocks water from flowing out of Raystown Lake at an area of low ground.

What are the risks associated with living near or downstream of Raystown Lake?

Although Raystown Dam reduces the risk of flooding to downstream communities, the dam does not eliminate the risk of flooding.  The most likely scenario that could result in downstream flooding from the dam would be a high-volume release of water from the dam’s spillways during significant storm events.  To maintain the structural integrity of the dam when the water level in the reservoir gets high, the spillways release water to the Raystown Branch Juniata River.  The frequency and amount of water being released could be great enough to cause flooding in downstream communities.  Such higher releases from the spillways could create conditions similar to how the river might behave if the dam did not exist.

There are also unlikely, but far more devastating, scenarios involving breach of the dam that would produce significant flooding.  This could involve situations such as: a rare, extreme rainfall event resulting in water flowing over the earthen dam, eroding the dam and leading to a breach of the dam; or unexpected behavior of seepage through the dam, eroding soil from within the embankment and leading to a breach of the dam.  If a breach were to occur, an uncontrolled surge of water would flow out of the reservoir, flooding downstream communities.  Huntingdon, Mapleton, Mt. Union, Lewistown, Shirleysburg, and adjacent communities are in the most immediate danger in the event of a flood.  Other communities along the Juniata River would also be impacted.

In any of the scenarios described above, the downstream floodwater would be swift and deep, overflowing levees and destroying buildings and key infrastructure. Those caught unaware and/or unable to evacuate could perish.  In the less likely dam breach scenarios, the water depth, property damage, and lives lost would likely be far greater.

Emergency Management Agency Contacts

Prepare your home and your family

Flood risk management is a shared responsibility. From federal, state, and local government to the individual level, we all have a role to play to reduce flood risk. 

Prepare your home and your family. Here are some ways you can proactively reduce risk:

  • Inform your family of dam failure flood risks, and make sure each family member knows what to do in the event of an emergency.
  • Seal basement walls with waterproofing compounds to avoid seepage.
  • Keep valued possessions and important papers on an upper level of your home or in a safety deposit box.
  • Prepare an emergency kit.
  • Know your evacuation routes.

What should you do in the event of an emergency?

If a flood is likely in your area, you should:

  • Listen to the radio or television for information.
  • Be aware that dam failure or operational flooding can occur.  Move to higher ground immediately. Do not wait for instructions to move. Get to high ground if flooding is imminent.

If you have to leave your home, remember these evacuation tips:

  • Do not walk through moving water. Six inches of moving water can make you fall. If you have to walk in water, walk where the water is not moving. Use a stick to check the firmness of the ground in front of you.
  • Do not drive into flooded areas. If floodwaters rise around your car, abandon the car and move to higher ground if you can do so safely. You and the vehicle can be quickly swept away.

Dam Risk Q&As

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  Are all dams hazardous? How hazardous is Raystown?

Dams are innately hazardous structures. Failure or mis-operation can result in a catastrophic release of water causing negative impacts upstream or downstream. Negative impacts of primary concern are the loss of human life, economic loss including property damage, lifeline disruption and environmental damage.

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Some dams are considered to have a greater hazard potential than others. As of 2021, there are approximately 16,500 high-hazard potential dams in the United States. Raystown Lake's Risk Assessment is categorized as "High".  "High-hazard potential" is a term used by a majority of state dam safety programs and federal agencies as part of a three-pronged classification system used to determine how hazardous a dam's failure might be to the downstream area.

While the definition varies from place to place, it generally means if failure of a high-hazard dam occurs, there probably will be loss of life. It must be emphasized that this determination does not mean that these dams are in need of repair - these dams could be in excellent condition or they could be in poor condition.  High hazard just reflects the dam's potential for doing damage downstream should it ever fail.

Dam failures or partial failures are not usually caused by storm events. Most failures fall into one or more of the following categories:

Structural failures: Foundation defects, including settlement and slope instability, or damage caused by earthquakes, have caused about 30 percent of all dam failures in the United States.

Mechanical failures: Malfunctioning gates, conduits, or valves can cause dam failure or flooding both upstream and downstream and account for about 36 percent of all dam failures in the United States.

Hydraulic failures: Overtopping of a dam is often a precursor to dam failure. National statistics show that overtopping due to inadequate spillway design, debris blockage of spillways, or settlement of the dam crest accounts for approximately 34 percent of all dam failures in the country.

These problems can lead to dam failure:

• Inadequate design criteria

• Malfunction of dam components

• Spillway damage or malfunction

• Seepage problems

• Embankment stability problems

• Damage from vandalism

• Improper operation

 How is dam risk classified? 

Common practice among federal and state dam safety offices is to classify a dam according to the potential impact a dam failure (breach) or mis-operation (unscheduled release) would have on upstream and/or downstream areas or at locations remote from the dam. The existing classification systems are numerous and vary within and between both the federal and state sectors. Although differences in classification systems exist, they share a common thread: each system attempts to classify dams according to the potential impacts from a dam failure or mis-operation, should it occur. The most significant problem with these various systems is the use of terms that lack clear definition. In addition, the various systems use different terminology to define similar concepts. This precludes consistency between the various federal and state agencies and understanding by the public.

Three classification levels are adopted as follows: LOW, SIGNIFICANT, and HIGH, listed in order of increasing adverse incremental consequences. The classification levels build on each other, i.e., the higher order classification levels add to the list of consequences for the lower classification levels. 

Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner’s property.

Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.

 How often is Raystown Lake inspected?

USACE has a robust Dam Safety Program that includes day-to-day inspections, as well as a more thorough annual inspection process. Large scale periodic inspections occur every five years. A multidisciplinary team led by a professional engineer, in conjunction with Baltimore District Operations personnel, performs periodic inspections at the project site. 

 I fish/camp/recreate at Raystown lake. How can I stay safe if there is a change in water level?

Raystown Lake uses a warning signal, or horn, to notify downstream public users of impending rapid increases or decreases in water levels that need to be made from the dam, which may lead to changes in flow that are unsafe for recreation. The signal can be heard from the dam to the main stream confluence (~5 miles). 

 What are some other online helpful resources?

Federal Emergency Management Agency - National Dam Safety Program

United States Department of Homeland Security - Dams Sector

United States Army Corps of Engineers - National Inventory of Dams

American Society Of Civil Engineers - Report Card on Dams

 What can I do to stay safe when recreating around a dam?

The most important thing to remember is keep your distance, keep your life. Steer clear of dam structures by recreating further up- or downstream, or portaging your kayak or canoe around the dam. Stay in designated recreation areas.  Dams are not intended to be playgrounds, and pose many risks. Always be aware of your surroundings, know the location of dams, stay away from dams, and wear a personal floatation device such as a life jacket.

If you chose to take advantage of the recreation at Raystown, make sure you follow these tips: 

  1. Know the area: Check maps or speak with locals to get information about hazards on that waterway. If swimming or fishing, always remain a safe distance from the structure to avoid sudden currents. If kayaking, canoeing, or boating, always portage around the structure or turn around well before reaching the dam to avoid being pulled over.
  2. Read the signs: Obey any and all posted signage and barriers in the area, including flood warnings, restricted access signs, portage signs, or other posted signs.
  3. Dress for danger: Wear a personal floatation device (such as a life jacket) if you are boating, fishing, swimming, or otherwise recreating in or around a waterway.
  4. Tell someone your plans: Let someone know, such as a friend or family member, when and to where you are heading out, and let them know when you return so they know you are safe.
  5. If you see someone in trouble, do not enter: Never enter the water yourself to try and help someone. Instead, call 911 and use a remote assistive device, such as a rope or throw bag, to try and pull them back to safety.

Click to learn about 16 Common Safety Hazards including hazards from water flows, human activities, environmental factors, and dam structures. 

 What does the Army Corps of Engineers do to reduce risk at Raystown Lake?

USACE performs ongoing activities to ensure the integrity of Raystown Lake Dam and to manage and reduce risk to downstream communities.  The dam is well maintained, inspected, and monitored. The frequency of inspection and monitoring increases during high water events.  USACE regularly updates the Emergency Action Plan for the dam and performs emergency response exercises with Federal, state, and local emergency managers to remain prepared to respond to flood events affecting the dam.  USACE also closely follows rainfall forecasts to determine when high water events may occur to provide information for any necessary flood warnings.

 What is the difference between floodplain maps and dam failure flood inundation maps?

Floodplain maps show the area expected to be inundated by floodwaters due to runoff from a rainfall event of a particular frequency from a riverine source. For example, Flood Insurance Rate Maps (FIRMs) published by the Federal Emergency Management Agency (FEMA) typically show the 1-percent-annual-chance (100-year) floodplain and sometimes a 0.2-percent-annual-chance (500-year) floodplain. The 1-percent-annual-chance floodplain is the area inundated by a flood having a 1-percent chance of being equaled or exceeded in a given year. FIRMs are utilized by communities who are participants in the National Flood Insurance Program to guide and regulate development. They are also utilized to determine flood insurance purchase requirements and rates.

Dam failure flood inundation maps show the estimated area expected to be flooded due to a failure or an uncontrolled release from a dam. These maps may consider different failure scenarios such as a non-rainfall-induced failure, also known as a sunny day or fair weather failure, or failure during a rainfall event. Dam failure flood inundation areas can be much larger than the 1-percent-annual-chance floodplain. The flood is more like a wave than a steady current and can have great power and force. Dam failure flood inundation maps are utilized by engineers and emergency managers to determine warning and evacuation areas downstream of a dam. It is important to note that dam failure flood inundation maps do not reflect the safety or integrity of a dam. Dams that meet safety regulations and are operated and maintained well may still have a dam failure flood inundation map.

Dam 101

What is a Dam?

A dam is a structure that is built across a river or body of water to hold, divert, or regulate water. Often the body of water stored behind a dam is referred to as the reservoir or lake. To see more dams across the U.S., go to Exploring Our Nation’s Dams.

What are the main parts of a dam? 

How do dams work? 

Dams are designed to regulate water for many uses, including managing flood risks up and downstream. Dams restrict water flow by holding it back or releasing it downstream. Some dams typically hold water behind them in a reservoir, while others are dry until there is a lot of rain. Whether the reservoir is typically dry or wet, it can only hold a finite amount of water.

When precipitation occurs upstream of the dam, water fills the reservoir and is slowly released through the dam. Once the water reaches a certain threshold in the reservoir, a spillway may be used to release more water. Some dams have an approved document or authorization that requires water to be spilled through the dam once it reaches a certain level within the reservoir.

Depending on the dam, spillways can either operate on their own or require an operator to decide when to use them. In either case, dam owners and operators typically know in advance if the dam will have to spill water and can work with up and downstream communities and emergency managers to give them advanced notice and support actions to protect people and property.

Many dams serve multiple purposes. This often requires those who operate dams to carefully monitor and manage the dam to try to provide all the intended benefits. For example, water may need to be held back and released in increments to support water supply or power generation, or water may need to be released to create space in advance of a large rain event.

Why are dams built?

Dams are built for multiple purposes and provide a variety of benefits. Some common benefits include the following:

  • Flood risk management – many dams are designed to collect, store, and release water. Catching or releasing water can help reduce flooding up and downstream of the dam.
  • Navigation – a series of dams and locks are used to support the safe transport of goods and materials on the inland rivers of the U.S.
  • Water Supply – many dams are used to store and supply water. In some cases, multiple dams on the same river may work as a system and can help lessen the impact of a drought or water shortage. Dams can also supply water for fire protection, agricultural production, or for industrial uses like cooling factory machinery.
  • Power generation– some dams generate power when water falls through the dam. The energy created by the water falling is captured by a generator and passed onto a nearby power grid.
  • Irrigation – both large and small dams have been built to help get water to crops and livestock. Large dams help do this by storing and providing more consistent access to water, while smaller dams on a farm, for example, are used to direct water where it is needed.
  • Recreation – lakes and rivers associated with dams provide outdoor recreation spaces to millions of visitors each year. Activities range from hiking and biking to fishing and boating.
  • Space for fish and wildlife – the reservoir or lake created by the dam and surrounding lands provide space for many aquatic species and migratory birds.
  • Waste management – some dams are built to contain industrial waste materials. These dams are often called tailing dams and are designed to keep materials from seeping into or damaging the surrounding environment.