Headwaters of the Minnesota River
Big Stone Lake was formed at the end of the last ice age when glacial Lake Agassiz drained through the gap into Glacial River Warren.
The valley of that river now holds Big Stone Lake.
The Lake covers 12,610 acres of surface area, is 26 miles long and averages about 1 mile wide.
Big Stone Lake is a border water, separating Minnesota and South Dakota.
The lake’s watershed* (highlighted in yellow to the left) is roughly
750 square miles, extending into North Dakota, South Dakota and Minnesota.
It is the source of the Minnesota River which flows 332 miles to the Mississippi!
*Watershed is a term used for all land that flows towards the same place*
The lake is fed by the Little Minnesota River
at its north end (watershed hi-lighted to the right),
and a number of tributaries on the
MN and SD side of the lake (shown above).
There are two state parks located at the lake—Big Stone Lake State Park on the Minnesota side as well as Hartford Beach State Park on the South Dakota side. Bonanza State Park is a secondary location on the MN side, where the Bonanza Education Center is located.
Fish populations include walleye, northern pike, bluegills, crappies and perch and another 30 or so species
There are 12 public accesses on Big Stone Lake.
The Big Stone Lake/ Whetstone Control Structure “Dam” (pictured left) was constructed in 1987 to control flows from the Whetstone River into the Minnesota River.
The Dam is located just south of the foot of the lake, below the confluence of the Whetstone River which flows in from South Dakota, since it was redirected in the 1930’s.
After the current Dam was constructed, there was interest in raising the summer lake level for recreational purposes.
A special permit was obtained, allowing the District to hold a summer pool of 968 project datum (pd) on Big Stone Lake from Spring to Fall each year
(one foot higher than the previous summer pool).
The historic outlet of Big Stone Lake was much lower than this newly established summer pool. In order to provide the necessary spring flood protection to homes and properties along the lake, the MN/ SD Boundary Waters Commission requires the District to lower the lake to 967 pd every fall.
The fall drawdown takes place in the month of October, allowing us to achieve winter pool before the lake freezes over.
For Questions on Dam Operations or Big Stone Lake elevations, please contact our Dam Superintendent at 320-839-3411.
To view up-to-date lake level readings, visit the Big Stone Lake Gage at this link National Weather Service Advanced Hydrologic Prediction Service
Click Here for MN DNR’s info page on Big Stone Lake
The Whetstone River Watershed is roughly 400 square miles. Historically this area flowed directly into the MN River, downstream of Ortonville, MN.
The Whetstone River was diverted in the 1930’s and currently outlets just upstream of the Big Stone Lake/ Whetstone River Dam- before entering the MN River.
As the elevation drops over 1,000 feet from the Coteau Hills to Big Stone City, SD it’s not unusual to see large increases in water come through this river system towards Big Stone Lake throughout the year.
More notably folks can see an increase in the Spring when we’re dealing with snow melting off the landscape within the frozen river.
Ice buildup can be seen near the Highway 12 bridge, just east of Big Stone City, where the land flattens out significantly before the Whetstone river heads towards the Big Stone Lake/ Whetstone Dam.
(check out our Whetstone Project Page for more information on this project)