Reservoirs in Washington
9 of 792 graded Washington lakes (1%) are man-made reservoirs in the USACE National Inventory of Dams. 6 carry a High or Significant hazard rating.
Reading the Washington reservoir landscape
Washington has 9 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 Washington'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 Washington reservoirs were built
All 9 Washington reservoirs (by surface area)
| Reservoir | County | Grade | Surface area | Year built | Purpose | Hazard |
|---|---|---|---|---|---|---|
| Banks Lake | Grant | A | 27,000 ac | 1951 | Flood Risk Reduction | High |
| Debra Jane Lake | Pierce | NR | 2,570 ac | 1911 | Recreation | High |
| Rimrock Reservoir | Yakima | C | 2,525 ac | 1925 | Flood Risk Reduction | High |
| Billy Clapp Lake | Grant | NR | 1,010 ac | 1948 | Flood Risk Reduction | High |
| Lacamas Lake | Clark | NR | 350 ac | 1936 | Recreation | High |
| Steilacoom Lake | Pierce | NR | 317 ac | 1989 | Fish and Wildlife Pond | High |
| Lake | Thurston | NR | 270 ac | 1951 | Recreation | Low |
| Lake | Thurston | C | 130 ac | 1955 | Recreation | Low |
| Moses Lake | Grant | B | — | 1961 | Irrigation | Low |
Frequently Asked Questions
How many reservoirs are in Washington?
9 of 792 graded Washington lakes (1%) are man-made reservoirs in the USACE National Inventory of Dams. 6 are rated High or Significant hazard, meaning failure would put downstream lives or property at substantial risk. The oldest matched dam dates to 1911.
What's the largest reservoir in Washington?
The largest matched reservoir in Washington is Banks Lake in Grant County at 27,000 acres of normal surface area, impounded by the North Dam (completed 1951).
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 LakeQuality 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 Washington reservoirs
Compare cabins, lodges, and vacation rentals near the largest reservoirs in Washington — live availability and prices for boating, fishing, and lake trips.
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More on reservoirs and water quality
Dam-built reservoirs and natural lakes graded side by side on the same nutrient and algae measurements — the gap, the reasons behind it, and the exceptions.
Surveyed maximum depth against A–F nutrient-and-algae grades: the pattern, the shallow lakes that still grade an A, and why land use beats bathymetry.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.
How phosphorus and nutrient runoff drive algae growth and turn lakes green, where the nutrients come from, and what it means for a lake's grade.
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 LakeQuality 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.