FAQ

What is a watershed?

A watershed is the area of land that drains into a particular lake, river or other waterbody. The Prior Lake – Spring Lake watershed is the land which drains into Prior and Spring Lakes. For a more detailed explanation, check out the ‘What is a Watershed?‘ page from the Mississippi WMO.

Watersheds can be big or small, depending on the scale at which you are looking; a watershed could be the land which drains into a small creek or the Mississippi River watershed which covers 40% of the continental United States. In fact, the Prior Lake – Spring Lake watershed is part of the larger Mississippi River watershed because Prior Lake outlets to the Minnesota River which then flows into the Mississippi River.

What is a watershed district?

Watershed districts are regional, special purpose units of government that work to solve, monitor and prevent water-related problems. The boundaries of each district follow those of a natural watershed and consist of the land in which all water flows to one outlet, such as a lake or river. Watershed districts are defined by MN Statutes and are created through a local petition process to the MN Board of Water and Soil Resources (BWSR). More information on Watershed Districts can be found on the BWSR website.

Though cities and townships often work together with watershed districts, they have different responsibilities. Cities provide the following types of water services: turning on or off water, processing water bills, providing drinking water, stormwater management, inspecting septic tanks, and beach monitoring (opening and closing).

The Prior Lake-Spring Lake Watershed District is not a part of the City of Prior Lake, Savage or Shakopee. The District partners with other local units of government including the local cities, townships, Scott County, tribal government, the soil and water conservation district, and the local school district, as well as local civic groups like the Prior Lake Association and Spring Lake Association. In Scott County, these local government units work together to ensure that collectively we are operating in an efficient and effective manner to provide the greatest benefit to our water resources.

Where is the Prior Lake-Spring Lake Watershed District? Do I live in the District?

Municipalities within the Prior Lake – Spring Lake Watershed District.

The Prior Lake-Spring Lake Watershed District encompasses 42 square miles of land including portions of the cities of Prior Lake, Savage and Shakopee; Spring Lake and Sand Creek townships; and parts of the Shakopee Mdewakanton Sioux Community.

To search your address, visit Scott County’s GIS map and search for your address. Once your property is selected, scroll through the parcel information window on the left hand side and look for the line that says “Watershed District” which will list the watershed you live in.

You can also visit the Mississippi WMO’s interactive map and enter your address to find out what watershed you live in! Feel free to contact us if you would like assistance determining whether you are in the District.

How long has the Prior Lake-Spring Lake Watershed District been around?

The Prior Lake-Spring Lake Watershed District was formed on March 4, 1970 at the request of local residents through a citizens’ petition. Visit our Watershed District Background page for a more complete history.

How is the Prior Lake-Spring Lake Watershed District governed?

The Prior Lake-Spring Lake Watershed District is governed by a board of five managers appointed by the Scott County Commissioners. The managers serve three year terms. All of the District’s policies, goals, and accomplishments are directed by the citizens who serve on the Board. The Board meets the second Tuesday of every month at 6:00 p.m., at the Prior Lake City Hall. Meetings are open to the public.

Visit our Board Members page for a list of current Managers and our Board Materials and Minutes page for a record of previous meetings. Meetings are recorded and on the Prior Lake television (PLTV) cable station. Recordings of previous meetings can be found on our YouTube page.

Where does the drinking water come from for cities and townships within the District?

Drinking water is supplied by the city, township, or tribal governments, or they are pumped from private wells. All of the municipalities within the District use water pumped form aquifers. Aquifers are underground layers of rock that are saturated with water and form natural storage areas for water which we then tap into.

Do I need a permit for my construction project?

You are required to obtain a permit from the Watershed District for any activity which disturbs one acre of land or more. However, if the disturbance activity is located within a shoreland protection zone (either within 1,000 feet of a lake or DNR-protected wetland, or within 300 feet of the Prior Lake Outlet Channel), a permit is required for an activity which disturbs more than 10,000 square feet (0.23 acres). Visit our Permit page for more information and permit applications.

What do I do if I see someone dumping into a waterbody or storm sewer?

Any input that is not comprised entirely of stormwater is considered an illicit discharge and should be reported to District staff. Illicit discharges come in many forms, including: yard waste, de-icing materials (such as salt), motor oil, pet waste, gasoline, paint, pesticides, and more. Often times it is our everyday actions which cause damage to local waters. For more information on illicit discharges, visit the Home and Yard page of our website.

If I am interested in planting a raingarden or shoreline restoration, does the District have any funds to help offset the costs?

Yes, the District has both incentive and cost share programs designed to provide some financial support. These programs are available for residential, agricultural, and commercial/industrial projects. To be eligible, projects must be approved prior to installation. See the Cost Share page under the Get Involved tab for more information.

Who is responsible for opening and closing beaches?

Individual cities decide when to open and close beaches. The only swimming beaches within the PLSLWD are operated by the City of Prior Lake. Please visit the City of Prior Lake’s Public Beaches page for more information.

Is that blue green-algae? How do I know if it’s safe to swim?

Cyanobacteria, better known as blue-green algae, can contain toxins (such as microsystin) that are unsafe for humans and pets. Not all blue-green algae contain toxins, but it is best to assume it does. When in doubt, best keep out! It is important to familiarize yourself with blue-green algae so you have a better idea when to avoid the water. The Minnesota Pollution Control Agency (MPCA) maintains a webpage with helpful information about blue-green algae and harmful algae blooms and shows pictures of blue-green algae.

Blue-green algae can take on different forms, but it has been described as looking like green paint, pea-green soup, or having a blue-green color. It can also have an unpleasant odor. Adults are usually offended by the sight and/or smell of algae which keeps them out of the water. However, children and dogs may not be as adverse to the algae so they need to be watched closely when blue-green algae is present.

There have been rare cases of microsystin poisoning even when no blue-green algae was visible. Based on that fact, the Prior Lake-Spring Lake Watershed District (District) can not confirm if blue-green algae is present for liability reasons. The District can try to help determine what type of algae is present by emailing pictures (info@plslwd.org), but they are not experts at algae identification and do not conduct site visits to identify algae types.

What can I do about the plants in the lake and along my shoreline?

Managing aquatic plants involves knowledge about plant type and role. While many water users prefer lakes free of vegetation, these plants play a vital role in the lake ecosystem and can even benefit recreation. Before removing aquatic plants it is important to determine whether they are beneficial or harmful to the lake. Visit our Shoreline page to learn more about which plants should be removed and how to manage your shoreline.

Note: No matter how close to shore, aquatic plants growing in public waters are owned by the State, which enforces strict regulations on vegetation removal, even for non-native and invasive species. Before attempting to control or remove any aquatic plants, contact your local Minnesota Department of Natural Resources office at (952) 496-4141. MN DNR staff can help identify plants, guide you through restrictions, and assist in identifying whether a permit will be required. To learn more about the DNR’s aquatic plant regulations and approved treatment methods, visit their website at: www.dnr.state.mn.us/apm/index.html.

Where can I find more information about what is being done regarding invasive species?

The MN DNR is the lead agency regarding invasive species in Minnesota (both aquatic and terrestrial invasive species). Their Invasive Species Department provides guidebooks on the identification of invasive species, tips on preventing their spread, related laws and regulations as well as an abundance of information on their programs.

What is the Spring Lake Outlet Channel, and who is responsible for it?

The Spring Lake outlet channel is a watercourse that connects Spring Lake to Upper Prior Lake. This channel is owned by Scott County, and the Watershed District does not have specific jurisdiction or rights over it. It is however, designated on the Public Waters Inventory which makes it a water of the state and gives the MN DNR regulatory jurisdiction.  Additional information on riparian rights and responsibilities, public access and other water law basics is available on the MN DNR Water Laws page.

The Spring Lake outlet does have a concrete weir (a small dam) in place about 20 feet from the lake edge, in the outlet channel. This structure was installed by Scott County in 1930 by a resolution of the County Commissioners. The purpose was to maintain a fixed minimum level below which water cannot flow out of the outlet (runout elevation). It was determined at the time of installation that the structure would not cause adversely high water levels on the lake.

How can I get involved with the District?

There are many ways to get involved – contact us, come to a district Board meeting, attend an informational workshop, or volunteer to be a part of the Citizen’s Advisory Committee. Visit the Get Involved page for more ideas.

Who controls the lake level?

The Prior Lake Outlet Structure allows water to discharge from Prior Lake once it reaches an elevation of 902.5 feet.

The elevation of Upper Prior and Lower Prior Lakes are predominantly controlled by natural processes of the water cycle including: precipitation– rain and snow falling directly on the surface of the lakes; surface runoff– rain or snow that falls on land and eventually runs into the lake through direct connections including from flow across properties and water from many streets and roads that is connected through the storm drain system; stream flow– when upstream water bodies increase in elevation and begin to flow downstream, such as Spring Lake flowing into Upper Prior Lake; groundwater interactions– both through discharge (water from underground aquifers welling up from an aquifer through springs) and recharge (water from the lake filtering down into the aquifer); evaporation– temperature, humidity, wind and even boat action all play factors in the rate of evaporation.

Upper and Lower Prior Lakes are landlocked and do not have a natural lake outlet. However, the Prior Lake Outlet System was constructed in 1983 to provide an artificial means to alleviate high water concerns and minimize flood damages. (See the Prior Lake Outlet System tab, below, or Prior Lake Outlet Structure page for further information). The DNR is ultimately in charge of lake elevations and requires the District to follow a DNR-approved operating plan and apply for permission to implement practices which significantly alter lake levels.

Why is Upper Prior Lake south of Lower Prior Lake? Aren’t they one lake?

While they are commonly referred to as one lake, Upper Prior and Lower Prior Lakes are considered two individual waterbodies by the MN DNR. The lakes were named based on the direction of water flow, rather than geographic location. Water from Upper Prior (upstream) flows into Lower Prior (downstream). The division between the two lakes is the County Road 21, at Wagon Bridge. The lakes used to be physically separated, and historic data shows different elevations for each lake. The lakes were named in honor of Charles H. Prior, superintendent of the Minnesota Division of the Milwaukee Railroad from 1871 to 1886.

Why is there a no wake ordinance and when is it in effect?

The City of Prior Lake has a Public Waters ordinance which authorizes the City Manager to enact a slow no-wake zone for Upper Prior and Lower Prior Lakes when the water elevation reaches or exceeds 903.90 feet above sea level. The ordinance remains in effect until the water elevation drops below 903.9 feet for three consecutive days. Spring Lake enters a slow no-wake restriction when the water elevation reaches or exceeds 912.8 feet above sea level.

There are also designated slow no-wake zones in several bays on Prior Lake. The goal of the ordinance is to moderate wave action caused by watercraft operation, to reduce erosion and property damage along the lakeshore.

The City of Prior Lake is responsible for determining the slow no-wake levels for the lakes. For more information visit the City of Prior Lake’s website.

Where can I find the current elevation of the lakes?

The Prior Lake-Spring Lake Watershed District has an automatic level logger which takes elevation readings on Prior Lake and Spring Lake. The elevation readings are automatically updated on the lake information pages of our website approximately every hour.

The automatic loggers are removed during the winter and are reinstalled once the ice is off the lake. Throughout the winter, district staff takes periodic manual readings at the staff gauge (a calibrated ruler used to measure water elevations) located on one of the pillars on the Wagon Bridge at County Road 21. Readings are updated on the website as they are taken.

If you are looking for historic elevation readings, visit the MN DNR Lakefinder website. The DNR lake number on each lake’s page on our website is linked to the Lakefinder page for that lake. All lake elevation readings collected by the District are submitted to the MN DNR and added to their database.

How much does the lake elevation change when it rains X amount? Is there a general rule it follows?

As much as it would be nice to have an established rule to determine how a certain amount of rainfall impacts lake elevation on Upper Prior and Lower Prior Lakes, there are many factors involved that prevent any sort of rule from being applicable in all situations. Some factors which play a part include:

• The intensity of the rainfall. One inch of rain over 30 minutes will impact the elevation much more than a one inch soaker rain received over 2 days.
• The duration of the rainfall, and its proximity to previous rainfalls. Has it been raining daily for 2 weeks or has there been a 2 month dry spell?
• Ground moisture conditions. Rock hard dry ground doesn’t absorb water well, whereas slightly damp soils allow water to soak in, at least until the soil becomes saturated.
• Upstream volume storage capacity. Are the ponds, wetlands, and lakes upstream rather low and will they “catch” the water before it gets to Prior Lake, or are they already full and any additional water will rush downstream; of specific note for Upper Prior and Lower Prior Lake is the level of Spring Lake.
• Temperature and humidity. The higher the temperature, the faster water will evaporate off of the lake. On the other hand, higher humidity means the air contains more water and as a result, it will be harder for water to evaporate from the lake.
• Wind and boat traffic. The more the surface of the water is stirred up and wavy, the more evaporation is going to occur.
• Groundwater interactions. The amount of groundwater discharge (water from underground aquifers welling up from an aquifer through springs) and recharge (water from the lake filtering down into the aquifer) occurring will also affect lake levels.
• Prior Lake Outlet Structure. Water flows over the weir in the Outlet Structure when the level of Prior Lake reaches 902.50 feet. The outlet can discharge up to 65 cubic feet of water per second.

Given all these variables, you can see that it is difficult to predict the way that the lake will respond to a given amount of rain. However, especially during very wet conditions, the elevation change on Prior Lake is greater than the volume of rainfall because every inch of rain that falls on the land also falls on the lake; flow comes in from Spring Lake; and runoff flows from the developed areas runs into the storm drain system and drains into the lake. This is why we continue to work to install projects that can provide additional treatment and storage of rainfall within the upstream watershed area, and in the area that immediately drains to the lake with direct runoff or storm sewer systems. The more we can keep the rain on the ground where it lands, rather than running off via roads and pipes, the closer we get to naturally-occurring hydrologic conditions, and the less the lake elevation increases in response to rainfall.

What is the Prior Lake Outlet System?

In 1973, citizens first petitioned the Prior Lake-Spring Lake Watershed District to construct a stormwater outlet from the landlocked Prior and Spring lakes. That year, a Feasibility Study concluded that a pipe outlet should be constructed as a relief valve to carry approximately 50 cubic feet per second of water downstream and that areas should be acquired and reserved for ponding purposes. This recommendation became what is known today as the Prior Lake Outlet System.

There are two key parts to the Prior Lake Outlet System. First, there is the Outlet Structure, which is located on Lower Prior Lake in the bay southwest of Martinson’s Island. It was originally installed in 1983 and was reconstructed with a more efficient design in 2010. The other component of the Outlet System is the seven-mile long Outlet Channel that begins with a short portion of underground pipe leaving the Outlet Structure that empties into an open channel near Jeffers Pond Elementary School. The Outlet Channel winds its way north (downstream) and eventually flows into the Minnesota River near Valleyfair in Shakopee.

Who owns it and who is responsible for it?

The Prior Lake-Spring Lake Watershed District owns and maintains the Prior Lake Outlet Structure. The operation of the Outlet Structure is governed by a MN DNR issued permit and approved management policies and operating procedures, including a set of strict parameters outlining when water is allowed to be discharged through the structure.

The Prior Lake Outlet Channel is governed by a cooperative agreement (signed in 2007) between the Prior Lake-Spring Lake Watershed District, the City of Prior Lake, the City of Shakopee and the Shakopee Mdewakanton Sioux Community. The Prior Lake-Spring Lake Watershed District is the administrating agency in active management of the Outlet Channel.

How does the Prior Lake Outlet Structure work?

Water enters the Prior Lake Outlet structure when the lake elevation reaches 901.50 feet, but it begins discharging at 902.50 feet.

The Prior Lake Outlet Structure has two fixed weirs (barriers, similar to a small dam). The external weir along the front opening of the Outlet Structure is at an elevation of 901.50 feet above sea level and is visible from the lake. As the lake elevation climbs above 901.5, the water begins to enter the inside of the Outlet Structure. However, water does not begin to discharge until it crests the internal weir at 902.50 feet above sea level as established by the MN DNR permit. Because the elevation of the weir is fixed, water is continuously discharging from the lake once it reaches 902.50 feet.

The accordion shaped design of the internal weir increases surface area compared to a straight weir. This increases the efficiency of water discharge.

The Outlet Structure is not designed to eliminate the possibility of flooding, but rather to reduce flooding potential. A simple way to visualize the design and the overall purpose of the Outlet Structure is to think of it like an emergency overflow on a bathtub. Once the water gets to the top, it automatically begins to flow out of the lake over the fixed weir. The weir is only in place to alleviate high water levels and will not drain the bathtub; neither will it entirely prevent flooding if the faucet is still on, but it will help reduce the level of flooding. For more information visit the Outlet Structure page of the website.

What is the low-flow gate, and how does that work?

The low-flow gate is a feature of the Outlet Structure which allows for manual discharge of water from Prior Lake when the lake elevation is below 902.50 feet. This is only done when it can be proven that it is necessary to draw down the lake. The District must follow its DNR-approved plan which outlines when the District is allowed to open the low-flow gate. The District is required to request permission from the DNR if it would like to open the low flow gate under conditions not outlined in the DNR-approved plan.

It is important to remember that even when the low flow gate is closed, the Outlet Structure discharges water continuously from Prior Lake once it reaches 902.50 feet.

Why can’t we leave the low-flow gate open all the time?

The District must follow its DNR-approved plan, which outlines when the District is allowed to open the low-flow gate, and must close the gate once the lake level drops to 902.5 feet. The District is required to request permission from the DNR if it would like to open the low flow gate under conditions not outlined in the DNR-approved plan.

Where does the water go once it leaves the lake?

Map of the Prior Lake Outlet Channel. Water travels from Prior Lake and the surrounding watershed, north, into the Minnesota River floodplain.

Water flows out the Outlet Structure into the Prior Lake Outlet Channel through a section of underground 36” diameter pipe. The pipe reaches the surface again just before Jeffers Pond Elementary School. From there the water from the lake begins to flow in an open surface channel. The Outlet Channel then goes through Upper and Lower Jeffers Ponds, crosses County Road 42, flows through a corner of Pike Lake and continues to head north. In the Riverside Bluffs neighborhood in Shakopee just north of County Road 16, the Outlet Channel turns to the west and flows into Dean Lake. Heading out of Dean Lake to the north again, crossing under Highway 169, the Outlet Channel passes by the west side of Quarry Lake. Eventually it flows under County Road 101, just to the east of Valleyfair, where it ends and empties into the Minnesota River floodplain.

From the point where the pipe surfaces, water running off from the adjacent landscape and through storm water systems also flows in the Prior Lake Outlet Channel. As a result, even if you see water flowing in the Outlet Channel, it does not always indicate that water is leaving Prior Lake.