Reservoirs in Pennsylvania
2 of 3 graded Pennsylvania lakes (67%) are man-made reservoirs in the USACE National Inventory of Dams. 2 carry a High or Significant hazard rating.
Reading the Pennsylvania reservoir landscape
Pennsylvania has 2 reservoirs in the USACE National Inventory of Dams — a limited count by national standards, reflecting the state's mix of natural lake topography and limited need (or political space) for major federal impoundments. Where reservoirs do exist, they tend to be either flood-control structures on smaller tributaries or municipal water-supply lakes — both with distinct access and recreation profiles.
Recreation is the headline purpose for the largest share of Pennsylvania's reservoirs — lakes where the dam exists explicitly to create surface water for fishing, boating, and adjacent shoreline development. Pool levels are typically maintained more stably than at flood-control or hydro reservoirs, which supports fixed-dock access, consistent boat ramps, and the kind of shoreline economy that natural-lake counterparts in the state share.
The USACE National Inventory of Dams (NID) catalogs every dam in the United States above a size threshold — typically 25 feet in height or 50 acre-feet in maximum storage, plus all dams classified as high-hazard regardless of size. The reservoir records below pull NID fields (year built, hazard class, maximum storage, surface area at normal pool, dam length, primary purpose) and pair them with water-quality data where the impoundment also appears in EPA's lake-monitoring inventory.
Why these Pennsylvania reservoirs were built
All 2 Pennsylvania reservoirs (by surface area)
| Reservoir | County | Grade | Surface area | Year built | Purpose | Hazard |
|---|---|---|---|---|---|---|
| Lake Nockamixon | Bucks | D | 1,450 ac | 1973 | Recreation | High |
| Lake Carey | Wyoming | D | 263 ac | 1876 | Recreation | High |
Frequently Asked Questions
How many reservoirs are in Pennsylvania?
2 of 3 graded Pennsylvania lakes (67%) are man-made reservoirs in the USACE National Inventory of Dams. 2 are rated High or Significant hazard, meaning failure would put downstream lives or property at substantial risk. The oldest matched dam dates to 1876.
What's the largest reservoir in Pennsylvania?
The largest matched reservoir in Pennsylvania is Lake Nockamixon in Bucks County at 1,450 acres of normal surface area, impounded by the Nockamixon (completed 1973).
What's the difference between a reservoir and a natural lake?
A reservoir is a body of water impounded by a man-made dam — typically built for flood control, hydroelectric power, water supply, irrigation, or recreation. A natural lake formed without human intervention, usually from glacial scouring, volcanic activity, or river meandering. Reservoirs typically have shoreline that fluctuates with seasonal water level management, while natural lakes have more stable shorelines. The USACE National Inventory of Dams classifies every regulated dam in the United States, which is how we identify which LakeGrade lakes are actually reservoirs.
What does the hazard class mean?
USACE assigns each dam a hazard potential classification based on what would happen downstream if the dam failed — NOT how likely the dam is to fail. "Low" hazard means dam failure would cause no probable loss of life and only low economic loss. "Significant" means probable loss of life is unlikely but appreciable economic damage would occur. "High" means probable loss of life and significant economic damage. The classification is about consequence, not condition. Many High-hazard dams are perfectly safe; they're rated High because populated areas have grown downstream over time.
Where does this reservoir data come from?
Every reservoir record on this page is matched to the USACE National Inventory of Dams (NID), the federal database of all dams ≥25 ft tall or impounding ≥50 acre-feet, plus any dam that poses a Significant or High hazard regardless of size. The NID is published by the U.S. Army Corps of Engineers and updated annually. Surface area, storage capacity, dam height, and hazard classification come directly from NID records.
Where to stay near Pennsylvania reservoirs
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Data source
Reservoir data from the USACE National Inventory of Dams (NID), the federal database of all regulated dams. Dam attributes (height, year completed, storage capacity, hazard class) are matched to LakeGrade lakes by proximity and dam-name similarity. Some lakes may be reservoirs that aren't matched if the dam record uses a name substantially different from our lake name.