Big Stone Lake 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
It is the source of the Minnesota River which flows 332 miles to the Mississippi!

The lake is fed by the Little Minnesota River at its north end, and a number of tributaries on the MN and SD sides.

There are two state parks located at the lake—Big Stone Lake Park on the Minnesota side and 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 for fishing use.

Flows out of the lake into the Minnesota River are regulated by the Big Stone Lake/ Whetstone River Dam at the southern end
Controlling Lake Levels

The Big Stone Lake/ Whetstone Control Structure (Dam) pictured above 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 1930s
(check out our Whetstone Project Page for more information on this project)

The Dam is operated by the District to hold a summer pool of 968 project datum (pd) 
from May through September each year.

The historic outlet of Big Stone Lake was much lower than this summer pool.
In order to provide the necessary protection to homes and properties along the lake, the MN/ SD Boundary Waters Commission requires the District to lower the lake back to the original outlet elevation every fall.

On October 1st of every year, the Dam Superintendent opens the dam gates, slowly releasing one foot of water from Big Stone Lake, to reach an elevation 
of 967 pd by the end of October.

This is known as the fall drawdown process. The lake is held at 967 pd through the winter, which provides a level of protection to properties along the lake,
 from the unpredictable Spring thaw, runoff and rain events 
that usually cause higher lake levels.