History of Grays Bay Dam

In the mid 1800’s the Dakota Mdewakanton village Reyataotonwe (Inland Village) was located on the southwest shore of Bde Maka Ska. The band’s chief was named Cloud Man, or Ma-hpi-ya-wi-ca-sta (Man of the Sky). Gideon and Samuel Pond set up a mission near the village in 1834 and taught the villagers to use European farming methods. In 1839, Chief Cloud Man and his band moved to Oak Grove (in present day Bloomington) to avoid conflict with the Ojibwe from the north and east. Another band camped annually on the peninsula between present day Gray’s Bay and Wayzata Bay to harvest wild rice. Chief Shakopee and his band camped on the site of present-day Wayzata.

In 1822, a pair of 17-year-olds at Fort Snelling military base became the first Europeans to record a trip to Lake Minnetonka. The two boys and two other soldiers canoed for two days and 22 miles up Minnehaha Creek to Lake Minnetonka. They camped on Big Island and returned to the fort the next day. Though Joe Brown built the first cabin in the watershed on the shores of Lake Minnetonka in 1826, he abandoned it a few years later and for the next 30 years, few Europeans ventured up the creek (then referred to as Brown’s Creek). The Dakota successfully kept the presence of their sacred Lake Minnetonka a relative secret from mapmakers. As late as 1850, government maps failed to show the lake.

It is no accident that most of the world’s great cities are built around great bodies of water. In the west metro, our communities sprang up along the waterfront as well, especially Lake Minnetonka and Minnehaha Creek.

European settlement of the area did not begin in earnest until 1851, when the treaties of Traverse des Sioux and Mendota transferred ownership of much of southern Minnesota and South Dakota from the Dakota people to the United States.

Minnehaha Creek – a much more powerful stream than the one we know today – became the site of several water-powered mills. The nucleus of the today’s cities formed around each mill and its accompanying roads and rail links. After the construction of the mill in 1852, the village of Minnetonka Mills became the easternmost port of Lake Minnetonka, two miles downstream of the lake, making the creek navigable up to that point.

As waterfront settlement progressed, residents encountered challenges with flooding. The construction of the first dam at Gray’s Bay in 1897 solved many of the flooding issues on the lake and creek. The new dam tamed the stream and ended the milling era, though many had already struggled to compete with the rise of steam power and the larger flow at St. Anthony Falls in Minneapolis.

Hennepin County built the dam at Gray’s Bay at 928.60 feet and establishes that Lake Minnetonka is to be maintained at 928.60 feet.

Through the 1930s, the area experienced the driest conditions in recorded history. During this period, the cities of Minneapolis and St. Paul expanded, but because this development occurred in a drier climate, there was little concern for flood risk.

In 1937, Lake Minnetonka reached it's lowest recorded level of 921.78 feet - nearly 8 feet below it's ordinary high water level of 929.4 feet.

Through the 1950’s, Minnesota’s urban landscape was changing quickly. Populations were booming and cities were racing to develop land and expand their tax bases, frequently draining wetlands to reclaim buildable area.

This draining of wetlands, combined with more hard surfaces (roads, parking lots, roofs) where open space used to be, caused rainwater that used to soak into the ground to run off the landscape. As a result, downstream communities faced new and serious flooding issues. Responding to these problems was complicated because most cities’ boundaries were drawn without regard to where water flows, and they managed water independently of each other despite their shared hydrological link.   

Swipe between the maps to explore land-use change, including the straightening and re-meandering of Minnehaha Creek, between 1953 (left) and 2018 (right). Credit: Hennepin County

The Minnesota Watershed Act was passed by the Minnesota Legislature in 1955. This novel idea established a special-purpose unit of local government to manage water within a watershed’s hydrological boundary. Citizens could petition for the establishment of a watershed district to manage water on a watershed-wide scale. 

In the mid-1960’s, communities along the flood-prone Minnehaha Creek were feeling the effects of landscape change. Following devastating flooding in the spring of 1966 residents along Minnehaha Creek in Minneapolis petitioned the Minnesota Board of Water and Soil Resources to form the Minnehaha Creek Watershed District (MCWD) to take a regional approach to managing water.

The first order of business for the newly-formed organization was managing how Lake Minnetonka drained into Minnehaha Creek. There had been some kind of fixed structure restricting the flow of water from the lake to the creek since the mid-1800s, but none managed the discharge. Water levels fluctuated at the mercy of Mother Nature, to the chagrin of people who lived along the lake and creek. 

Creating an adjustable dam at the Gray’s Bay outlet to Minnehaha Creek, and a plan to guide its operation, was a complicated task. It took nearly ten years of extensive scientific and historical research to develop an operating plan that mimicked the pre-settlement outlet conditions of Lake Minnetonka. Many communities and organizations were involved in the process.

A new adjustable dam was constructed in 1979. It was updated in 2006 to include a viewing/fishing deck and to connect it to a trail built by the City of Minnetonka. The shoreline was restored and signage was also installed. 

In 2014, the Twin Cities saw the wettest first half of the year since modern day record keeping began in 1871.

Coupled with a long winter and late snow melt, this extreme precipitation led to record water levels in 26 lakes and streams and more than $1 million worth of damages along the six main streams in the Minnehaha Creek Watershed District. For 83 consecutive days, Gray’s Bay Dam was unable to control water levels on Lake Minnetonka or Minnehaha Creek because the dam was underwater.

Swipe between the images of Grays Bay Dam to view the change in water level from May 1, 2014 (left) and June 20, 2014 (right).

On June 23, 2014, Lake Minnetonka reached a record elevation of 931.11 feet above sea level, more than seven inches higher than the previous record, and Minnehaha Creek achieved a record flow of 889 cubic feet per second.

Since then, the Twin Cities has also broken other precipitation records:

• 2016 was the second wettest full year on record
• August 2016 – July 2017 was the wettest 12-month period on record
• 2019 was the wettest year on record

After the significant flooding in 2014 and facing climate change and increasingly unpredictable weather, MCWD formed a formal partnership with the National Weather Service, Hennepin County, and the U.S. Geological Survey (USGS) with the goal of better anticipating rain events and understand their effects on water levels to manage the Gray’s Bay Dam more proactively. As part of this multi-agency partnership, the USGS, NWS, and Hennepin County provide:

• Real-time water level readings on Minnehaha Creek and Lake Minnetonka
• Seven-day precipitation forecasts, in six-hour increments, for the 125-square mile area that drains to Lake Minnetonka
• Hydrologic inflow model which predicts how the forecasted precipitation will flow into Lake Minnetonka from the upper watershed streams
• Lake level simulation model which forecasts how the predicted inflow will affect the Lake Minnetonka water elevation
• Real-time precipitation and weather attributes

This information allows MCWD to plan and moderate dam discharge before large rain events based on the predictive Lake Minnetonka area forecast. This allows the District to proactively increase discharge before large rain events to create space in Lake Minnetonka for the forecasted precipitation. Similarly, MCWD can reduce discharge right before large rain events to provide capacity in Minnehaha Creek for runoff . This reduces the flow of water into the creek, preventing flooding in downstream communities. During dry periods, dam discharge is adjusted in an effort to keep water flowing into Minnehaha Creek so the creek doesn’t run dry.

The success of this partnership was highlighted in 2016, which was the wettest year on record in the Minnehaha Creek watershed. Due to information provided by the National Weather Service, Hennepin County, and USGS we were able to operate the dam proactively and prevent flooding on Lake Minnetonka or Minnehaha Creek, despite the record-breaking rainy weather.