A red sun low over Slim Lake through wildfire haze, its reflection a column of orange on the water

Reservoirs in Wisconsin

187 of 3,133 graded Wisconsin lakes (6%) are man-made reservoirs in the USACE National Inventory of Dams. 83 carry a High or Significant hazard rating.

Reading the Wisconsin reservoir landscape

Wisconsin hosts 187 man-made reservoirs in the USACE National Inventory of Dams — a dense reservoir landscape that reflects significant federal, state, and utility-led impoundment construction over the 20th century. Reservoir lakes behave differently than natural lakes: water levels are managed for the dam's primary purpose, residence time depends on inflow and release schedules, and depth profiles follow the original river-valley topography rather than the bowl shape of glacial lakes.

Recreation is the headline purpose for the largest share of Wisconsin'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 Wisconsin reservoirs were built

138

Recreation

Hydroelectric

Other

Flood Risk Reduction

Navigation

Fish and Wildlife Pond

Water Supply

187

Total reservoirs

171,099

Total surface acres

1,199,173

Normal storage (ac-ft)

High or Significant hazard

All 187 Wisconsin reservoirs (by surface area)

Reservoir	County	Grade	Surface area	Year built	Purpose	Hazard
Turtle Flambeau Flowage Lake	Iron	B	13,798 ac	1926	Hydroelectric	High
Billy Boy Flowage Lake	Sawyer	B	8,464 ac	1936	Recreation	Significant
Lake Dubay	Marathon	D	7,800 ac	1942	Hydroelectric	High
City Millpond	Green Lake	NR	7,346 ac	1869	Recreation	High
Beaver Dam Lake	Dodge	D	6,542 ac	1840	Recreation	High
Lake Wissota	Chippewa	D	6,212 ac	1917	Hydroelectric	High
Lake Waubesa	Dane	B	5,448 ac	1938	Navigation	Low
Holcombe Flowage Lake	Chippewa	D	4,300 ac	1950	Hydroelectric	High
Rest Lake	Vilas	NR	4,200 ac	1925	Recreation	High
Gile Flowage Lake	Iron	C	3,317 ac	1941	Other	High
Long Lake	Washburn	B	3,290 ac	1913	Recreation	High
Namekagon Lake	Bayfield	NR	3,208 ac	1886	Recreation	High
Danbury Flowage Lake	Burnett	NR	2,800 ac	1928	Hydroelectric	Low
Lake Kegonsa	Dane	D	2,716 ac	1938	Navigation	Low
Chequamegon Waters Flowage Lake	Taylor	D	2,714 ac	1967	Recreation	High
Fox Lake	Dodge	D	2,625 ac	1838	Recreation	Low
Nelson Lake	Sawyer	B	2,503 ac	1936	Recreation	Low
Pewaukee Lake	Waukesha	B	2,493 ac	1842	Recreation	High
Lake Noquebay	Marinette	B	2,409 ac	1929	Recreation	Low
Birch Lake	Washburn	C	2,288 ac	1878	Recreation	Significant
Birch Lake	Sawyer	D	2,288 ac	1878	Recreation	Significant
Buffalo Lake	Marquette	D	2,210 ac	1922	—	Low
Lake Montello	Marquette	NR	2,210 ac	1922	—	Low
Delavan Lake	Walworth	C	2,072 ac	1935	Recreation	Low
Dairyland Reservoir	Rusk	NR	1,952 ac	1951	Hydroelectric	High
Saint Croix Flowage Lake	Douglas	B	1,913 ac	1854	Recreation	Low
Spirit River Flowage Lake	Lincoln	D	1,698 ac	1922	Hydroelectric	High
Moose Lake	Sawyer	C	1,670 ac	1897	Recreation	High
Minong Flowage Lake	Washburn	C	1,609 ac	1936	Recreation	High
Lake Menomin	Dunn	D	1,405 ac	1957	Hydroelectric	High
Rock Lake	Jefferson	B	1,371 ac	1865	Recreation	High
Bear Lake	Barron	B	1,358 ac	1880	Recreation	Low
Legend Lake	Menominee	B	1,304 ac	1968	Recreation	High
Long Lake	Price	NR	1,237 ac	1934	Recreation	High
Wilson Flowage Lake	Price	D	1,237 ac	1934	Recreation	High
Island Lake	Rusk	B	1,222 ac	1875	Recreation	Low
Little Rice Lake	Forest	NR	1,219 ac	1936	Recreation	Low
Clam Lake	Burnett	D	1,207 ac	1936	Recreation	Low
Beaver Dam Lake	Barron	B	1,163 ac	1942	Recreation	Low
Spooner Lake	Washburn	B	1,092 ac	1884	Recreation	Significant
Yellow River Flowage Lake	Washburn	B	1,092 ac	1884	Recreation	Significant
Upper Eau Claire Lake	Bayfield	B	1,030 ac	1950	Recreation	Low
Caldron Falls Reservoir	Marinette	NR	1,018 ac	1924	Hydroelectric	High
Twin Falls Flowage Us Twin Falls Dam Lake	Florence	NR	960 ac	1960	Hydroelectric	High
Wind Lake	Racine	C	936 ac	1905	Recreation	Low
Sand Lake	Sawyer	A	928 ac	1950	Recreation	Low
Nagawicka Lake	Waukesha	B	917 ac	1936	Other	Low
Middle Eau Claire Lake	Bayfield	B	902 ac	1939	Recreation	Significant
Rice Lake	Barron	C	860 ac	1864	Hydroelectric	High
Solberg Lake	Price	C	859 ac	1940	Recreation	Low
Mason Lake	Adams	D	856 ac	1850	Recreation	High
Lake Beulah	Walworth	A	834 ac	1840	Recreation	High
Mill Lake	Walworth	B	834 ac	1840	Recreation	High
Tiger Cat Flowage Lake	Sawyer	B	819 ac	1937	Recreation	Significant
Alexander Lake	Lincoln	D	803 ac	1913	Hydroelectric	High
Lower Eau Claire Lake	Bayfield	B	802 ac	1938	Recreation	Low
Webb Lake	Burnett	NR	759 ac	1941	Recreation	Low
Oconomowoc Lake	Waukesha	B	721 ac	1899	Recreation	Low
Altoona Lake	Eau Claire	D	720 ac	1938	Recreation	High
Neshonoc Lake	La Crosse	NR	687 ac	1914	Hydroelectric	Low
Flynn Lake	Bayfield	NR	650 ac	1941	Recreation	Low
Inch Lake	Bayfield	NR	650 ac	1941	Recreation	Low
Hat Rapids Flowage Lake	Oneida	NR	640 ac	1923	Hydroelectric	High
Whitewater Lake	Walworth	B	640 ac	1925	Recreation	Low
North Twin Lake	Polk	B	639 ac	1888	Recreation	High
South Twin Lake	Polk	NR	639 ac	1888	Recreation	High
Apple River Flowage Lake	Polk	D	639 ac	1888	Recreation	High
Reservoir Pond	Oconto	B	618 ac	1877	Recreation	High
Lake Redstone	Sauk	D	612 ac	1967	Recreation	High
Callahan Lake	Sawyer	B	602 ac	1938	Recreation	Low
Little Lake Butte des Morts	Winnebago	D	582 ac	1940	Flood Risk Reduction	Significant
Musser Lake	Price	D	563 ac	1936	Recreation	Low
Rock River Lake	Rock	NR	548 ac	1927	Hydroelectric	Low
Lower Phantom Lake	Waukesha	B	540 ac	1848	Recreation	Low
Pike Lake	Washington	B	522 ac	1870	Recreation	Low
Eagle Lake	Racine	D	515 ac	1917	Recreation	Low
Little Muskego Lake	Waukesha	NR	506 ac	1972	Recreation	High
Nepco Lake	Wood	B	494 ac	1926	Water Supply	Low
Townsend Flowage Lake	Oconto	B	476 ac	1880	Recreation	High
Trego Lake	Washburn	NR	470 ac	1927	Hydroelectric	Significant
Yellowstone Lake	Lafayette	D	455 ac	1953	Recreation	High
Camelot Lake	Adams	B	445 ac	1969	Recreation	High
Chute Pond at	Oconto	C	440 ac	1937	Recreation	High
Upper Park Falls Flowage Lake	Price	NR	432 ac	1916	Hydroelectric	Low
Long Lake	Fond du Lac	B	427 ac	1857	Recreation	Significant
Crowley Flowage Lake	Price	NR	422 ac	1930	Hydroelectric	High
Killarney Lake	Oneida	NR	421 ac	1961	Recreation	Low
Clam River Flowage Lake	Burnett	NR	360 ac	1944	Hydroelectric	Low
Lake Eau Galle	Dunn	D	350 ac	1913	Hydroelectric	Low
Lake Wingra	Dane	B	345 ac	1930	Recreation	Low
Fishtrap Lake	Vilas	B	339 ac	1884	Recreation	High
Lake of the Falls	Iron	B	338 ac	1895	Recreation	Low
Spring Lake	Columbia	D	312 ac	1849	Recreation	High
Park Lake	Columbia	NR	312 ac	1849	Recreation	High
Eagle Spring Lake	Waukesha	B	311 ac	1836	Recreation	Significant
Arrowhead Lake	Adams	B	300 ac	1978	Recreation	Low
Dexter Lake	Wood	D	298 ac	1964	Recreation	Low
Amacoy Lake	Rusk	C	278 ac	1967	Flood Risk Reduction	Low
Lake Mallalieu	St. Croix	D	270 ac	1866	Recreation	Low
Lower Nemahbin Lake	Waukesha	B	268 ac	1934	Recreation	Low
Lake Delton	Sauk	NR	267 ac	1927	Recreation	Low
Mcdill Pond	Portage	C	261 ac	1855	—	Significant
Hancock Lake	Oneida	C	259 ac	1930	Recreation	Low
Lake Sherwood	Adams	B	246 ac	1968	Recreation	Significant
Minerva Lake	Burnett	B	245 ac	1937	Recreation	Low
Loon Lake	Burnett	B	228 ac	1938	Recreation	Low
Lake Tomah	Monroe	D	225 ac	1936	—	High
Lawrence Lake	Marquette	C	221 ac	1845	Hydroelectric	Low
Pickerel Lake	Oconto	B	220 ac	1960	Recreation	Low
Black Hawk Lake	Iowa	B	220 ac	1969	Recreation	Low
Lily Lake	Forest	NR	213 ac	1976	Recreation	Low
Iola Lake	Waupaca	B	206 ac	1865	Recreation	Significant
Big Roche A Cri Lake	Adams	B	204 ac	1924	Recreation	High
Little Tamarack Flowage Lake	Vilas	B	200 ac	—	—	Low
Baker Lake	Vilas	C	200 ac	—	—	Low
Myrtle Lake	Vilas	B	200 ac	—	—	Low
Pixley Flowage Lake	Price	NR	193 ac	1918	Hydroelectric	High
Murphy Flowage Lake	Rusk	C	188 ac	1994	Recreation	Low
Big Moon Lake at	Barron	B	187 ac	1968	Recreation	Low
Lake Shangri-la	Kenosha	NR	172 ac	1927	Recreation	High
Comus Lake	Walworth	D	164 ac	1947	Recreation	Low
Pigeon Lake	Waupaca	D	163 ac	1855	Recreation	Low
Lazy Lake	Columbia	D	161 ac	1859	Recreation	Significant
Vern Wolf Lake	Kenosha	NR	158 ac	1972	Recreation	Low
Long Trade Lake	Polk	D	153 ac	1874	Recreation	Significant
Radigan Flowage Lake	Douglas	D	150 ac	1938	Recreation	High
Wazeecha Lake	Wood	NR	148 ac	1939	Recreation	High
Townline Lake	Oneida	C	144 ac	1941	Recreation	High
Maple Lake	Oneida	B	144 ac	1941	Recreation	High
Mirror Lake	Sauk	D	137 ac	1931	Recreation	Low
Rice Lake	Walworth	D	137 ac	1968	Recreation	High
Blue Spring Lake	Jefferson	B	136 ac	1928	Recreation	High
Waubeesee Lake	Racine	NR	129 ac	1924	Recreation	Low
Dutch Hollow Lake	Sauk	B	125 ac	1971	Recreation	Low
School Section Lake	Waukesha	B	117 ac	1937	Recreation	Low
Nugget Lake	Pierce	C	116 ac	1973	Flood Risk Reduction	High
Friendship Lake	Adams	C	114 ac	1928	Recreation	Significant
White Mound Lake	Sauk	C	104 ac	1970	Flood Risk Reduction	Low
Black Brook Flowage Lake	Polk	D	98 ac	1917	Hydroelectric	Low
Grindle Lake	Oconto	B	95 ac	1944	Fish and Wildlife Pond	Significant
Little Sand Lake	Barron	C	94 ac	1940	Other	Low
Wyona Lake	Columbia	D	93 ac	1849	Recreation	Low
Hallie Lake	Chippewa	NR	83.7 ac	1908	Recreation	Low
Jordan Pond	Portage	C	83 ac	1850	Recreation	Low
Peppermill Lake	Adams	C	80 ac	1969	Recreation	Low
Cruson Slough Lake	Richland	C	80 ac	—	Recreation	Low
Alpine Lake	Waushara	B	80 ac	1970	Recreation	Low
Sidie Hollow Lake	Vernon	NR	78 ac	1965	Flood Risk Reduction	Low
Fowler Lake	Waukesha	B	78 ac	1840	Recreation	Significant
Forestville Millpond	Door	D	72 ac	1877	Recreation	Low
Lake Esadore	Taylor	B	71 ac	1900	Recreation	Low
Lower Park Falls Flowage Lake	Price	NR	71 ac	1923	Hydroelectric	Low
Pella Lake	Shawano	NR	69 ac	1883	Recreation	Low
Henrietta Lake	Waukesha	NR	68 ac	1962	Recreation	Low
White River Pond	Waushara	NR	64 ac	1923	Recreation	Low
Spring Lake	Waukesha	B	60 ac	1966	Recreation	Low
Bakkens Pond	Sauk	B	60 ac	1968	Other	Low
Ludden Lake	Iowa	D	58 ac	1964	Recreation	Low
Arkdale Lake	Adams	B	55 ac	1860	Recreation	Low
Amherst Millpond	Portage	C	48 ac	1857	Recreation	Significant
Chilton Millpond	Calumet	D	46 ac	1850	Recreation	High
Thiensville Millpond	Ozaukee	NR	45 ac	1842	Recreation	Low
Rock Lake	Kenosha	B	44 ac	1929	Recreation	Low
Honey Lake	Walworth	D	44 ac	1952	Recreation	Low
Leota Lake	Rock	D	41 ac	1950	Recreation	High
Bernice Lake	Fond du Lac	D	35 ac	1840	Recreation	Low
Grafton Millpond	Ozaukee	NR	35 ac	1918	Recreation	Significant
Mcginnis Lake	Adams	B	33 ac	1966	Recreation	Low
Antigo Lakes	Langlade	NR	32 ac	1936	Recreation	Low
Unnamed Lake	Iron	NR	31 ac	1968	Recreation	Low
Spruce Lake	Oneida	NR	30 ac	1967	Other	Low
Eddy by Pony Creek Lake	Shawano	NR	28 ac	1910	Recreation	High
Tilleda Off Bridge Lake	Shawano	NR	28 ac	1910	Recreation	High
Tilleda Pond	Shawano	D	28 ac	1910	Recreation	High
Easton Lake	Adams	D	24 ac	1855	Recreation	Low
Marl Lake	Waupaca	B	22 ac	1939	Recreation	Low
Hidden Valley Lake	Lafayette	D	22 ac	1975	Recreation	Low
Pope Lake	Waupaca	B	22 ac	1939	Recreation	Low
Fawn Lake	Adams	B	19 ac	1972	Recreation	High
Cranberry Lake	Oneida	C	18 ac	—	Recreation	Low
Springville Pond	Portage	B	18 ac	1850	Recreation	High
Fairchild Pond	Eau Claire	NR	18 ac	1955	Recreation	Low
Fountain Lake	Portage	NR	16 ac	1938	Recreation	Low
Park Creek Pond	Douglas	NR	11 ac	1972	Other	Low
Lac Vieux Desert Lake	Vilas	C	—	1907	Hydroelectric	Low
Fawn Lake	Vilas	NR	—	1923	Hydroelectric	Low
Minocqua Lake	Oneida	B	—	1909	Hydroelectric	Low

Frequently Asked Questions

How many reservoirs are in Wisconsin?

187 of 3,133 graded Wisconsin lakes (6%) are man-made reservoirs in the USACE National Inventory of Dams. 83 are rated High or Significant hazard, meaning failure would put downstream lives or property at substantial risk. The oldest matched dam dates to 1836.

What's the largest reservoir in Wisconsin?

The largest matched reservoir in Wisconsin is Turtle Flambeau Flowage Lake in Iron County at 13,798 acres of normal surface area, impounded by the Turtle-Flambeau (completed 1926).

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 Wisconsin reservoirs

Compare cabins, lodges, and vacation rentals near the largest reservoirs in Wisconsin — live availability and prices for boating, fishing, and lake trips.

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More on reservoirs and water quality

Are Reservoirs Cleaner Than Natural Lakes?

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.

Do Deeper Lakes Have Better Water Quality?

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.

Lake Water Quality Grades Explained: What A–F Means

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.

Why Lakes Turn Green: Phosphorus and Nutrient Pollution

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.