Long Lake Questions and Answer

LLISA often receives questions about Long Lake. Here are answers for residents regarding lake levels.

Where can I find lake level information?How does hydrology work for Long Lake?
  • Long Lake depends on water flowing in from Manitou Creek, Eagle Creek and Round Lake Drain, which drain 39 square miles or 24,000 acres of Lake County.
  • Water flows through Long Lake and discharges downstream through Manitou Creek where it flows over the Long Lake dam which is approximately 24 inches higher than the Chain O’ Lakes.
  • The dam system is designed to naturally self-level under normal flow conditions; when more water flows in, more water flows out and alternately when inflow slows, outflow slows.
What impacts water levels in Long Lake?
  • The main spillway at the dam is the primary factor that controls the lake level. This structure has been unchanged since its construction in 1930
  • Higher water levels are likely to occur as a result of moderate to severe rain events and ice melt across the 24,000 acre watershed.
  • High inflow from Manitou Creek, Eagle Creek and the Round Lake Drain causes water level in Long Lake to rise as flow increases.
  • Decrease in flow and related drought conditions cause water to drop to the level of the dam spillway, or possibly lower, a result of evaporation and leakage through the dam.
What is the typical water level of Long Lake?
  • Normal Water Level is reported to be 739+/- feet above sea level according to historical documents, official lake reports and county records.
  • The top of the spillway is at an elevation of 738.7 feet above sea level.
  • Typical range of water levels under normal conditions is 738.8 – 739.5, a variance of approximately 9 inches.
How long does water stay in Long Lake?
  • Hydrologic retention is about one month according to Lake County Health Department reports.
Is Long Lake drawn down in the winter like the Chain O’Lakes?
  • No, Long Lake attempts to keep a consistent water level all year.
What are the challenges for Long Lake?
  • Long Lake is part of a complex watershed that stretches 40 square miles, one of the largest in the county.
  • Weather is unpredictable. Extremes of drought and heavy rainfall are more common.
  • Continued land development in Manitou Creek Watershed leads to Long Lake receiving more water, more quickly, when storm events occur.
  • When high inflow occurs, the lake swells with three inputs and only one output.
  • Flooding can also be experienced by water backing up from the Chain O Lakes and Fox River.
  • Nutrient pollution and introduced sediment from high water events contribute to harmful bluegreen algae blooms and decreased water clarity.
  • There is no way to predict drought or defend against low water resulting from drought conditions.
What are the components of the Long Lake dam?
  • Main spillway – 22.5 feet wide, elevation 738.7
  • Boat slip – 9 feet wide, elevation 738.9
  • Sluice gate – 11 feet wide, elevation 739.1
What is the sluice gate?
  • Rotating steel gate that can be opened to discharge excess water during high flow/high water events.
  • Used to alleviate the risk of flooding.
How is the decision made to use the sluice gate?
  • A committee of board members makes the call depending on many factors that impact watershed conditions, including detailed weather forecasting and data from Stormwater Management Agency, ground moisture, flow, current water levels, height differential with the Chain O’Lakes, historical data, seasonal expectations, and ice coverage.
  • When used, the gate is typically opened anywhere from hours to days depending on flow and can be partially to fully opened as needed.
  • The sluice gate is opened to prevent high water and flooding which protects property, ensures public safety, and limits environmental degradation.
  • The gate is typically used in early spring to manage high flow due to precipitation and ice melt.
Why is active management, including use of the sluice gate, important?
  • High water levels cause severe erosion which damages property and harms lake ecology
  • High water levels cause unsafe conditions at the dam and boat slip
  • High water levels cause undue stress on the dam system which is nearly 100 years old
  • Flood control requires proactive response. Once flooded, there is no way to quickly correct.
  • LLISA has been properly using the sluice gate to protect community interests since its installation over 50 years ago.
Doesn’t opening the sluice gate lead to low water levels?
  • No, the sluice gate is only opened in times of heavy inflow and provides only short-term impact on water level.
  • Water level is always in the typical range (739 -739.5) after the gate is closed.
  • The sluice gate is used to help avoid flood conditions.
Can’t we keep water levels higher all the time?
  • Water level is based on the height of the spillway (738.7) and inflow from the watershed.
  • Water levels do not stay high without necessary inflow from the watershed.
  • Higher water causes increased outflow over the dam as the water seeks equilibrium, making it impossible to sustain high water levels without additional inflow from the watershed.
  • The lake level quickly reverts to normal levels under normal flow conditions.
  • The system does not allow for extra water to be retained for times of drought or low flow.
Why is my channel so shallow?
  • Most channels around Long Lake were dredged between 1900-1930 to be about 30 feet wide and 5 feet deep.
  • Some channels have silted in over the past 100 years such that some are now difficult to navigate by power boat.
  • LLISA wants to help and has consulted with property owners regarding dredging projects in the past. Small scale dredging projects are very difficult, however, as permitting is a challenge, the process is very expensive and channels may be either privately or publicly owned.
What has LLISA learned from having real time lake level data?
  • The lake level is always seeking equilibrium between inflow and outflow. Lake level is rarely static, water level is always going up or going down depending on flow.
  • We have greatly improved our ability to predict crest water height and duration for high water events.
  • Water levels higher than 739.5 significantly decrease the ability to mitigate flood risk.
What was observed from drought conditions in 2021, 2022 and 2023?
  • Low water levels in 2023 allowed LLISA to inspect the dam structure below the typical water line. The spillway required minor repair, which is in process. This repair will help the dam retain water during times of low flow.
  • Low flow during spring and early summer reduced incoming sediment and nutrient pollution, allowing for clearer water.
  • Fewer harmful algal blooms in 2022 & 2023 as compared to previous years.
  • Most lakes in northern Illinois have experienced lower levels due to drought.
What agencies does LLISA collaborate with regarding lake management?
  • Lake County Health Department
  • Lake County Stormwater Management Agency
  • Lake County Forest Preserve
  • Lake County Board
  • Grant Township
  • Avon Township
  • Illinois Environmental Protection Agency
  • United States Geological Survey
  • Illinois State House of Representatives
  • Illinois Senate
  • Army Corps of Engineers
Ready for more – Research Articles, Technical Reports and further readingHistorical ReferenceDocuments referring to Long Lake water level
  • 1969 Long Lake Bathymetric map indicates Long Lake elevation as 739' MSL or mean sea level, an antiquated term referring to the average water level.
  • 2001 Summary Report of Long Lake as completed by Mike Adam and Mark Pfister, Lake County Health Department. Page 5 states elevation to be 739' above sea level.
  • 2004 Manitou Creek Watershed Plan states: Long Lake’s normal water elevation of 739.0 NGVD is the same as it was in 1920, page 5-25. Table 5-16 on page 5-35 states Long Lake’s normal water elevation and conveyance is the same now as when a dam was installed in 1930.
  • 2006 Stanley Consulting Engineering plans for Long Lake dam and seawall repair, approved by Building and Zoning and Army Corps of Engineers. Starting on page 4 the normal water level or NWL is shown as 738.8 and is repeated throughout the document.
  • 2007 Summary Report of Long Lake prepared by the Lake County Health Department Environmental Services Lakes Management Unit as completed by Leonard Dane, Michael Adam, Shaina Keseley and Adrienne Orr. Page 1, Lake Facts, states the elevation as 738.0 feet
  • 2008 Summary Report of Long Lake prepared by the Lake County Health Department Environmental Services Lakes Management Unit as completed by Leonard Dane, Michael Adam, Kelly Deem and Kathleen Paap. Page 1, Lake Facts, states the elevation as 738.0 feet
  • FEMA Manitou Creek Flood Profile shows 10 year flood elevation at approximately 740'.
  • 1978 Plat of Survey Pickerel Point displays water elevation at 739
  • 1981 Plat of Survey Pickerel Point displays water elevation at 738.3
  • 1985 Plat of Survey Pickerel Point displays water elevation at 738.56

LLISA Automated Water Level Monitoring Project

Scope
  • To be able to remotely monitor Long Lake water levels in real time
  • To eliminate the painstaking manual collection of data and expand the number of water level data points and locations we monitor
  • Provide data directly to the LLISA website for easy viewing and analysis
  • To maintain a historical record of the levels year over year for better prediction in the future
  • To learn more about our lake and how it is affected by weather events and seasonal cycles.
  • To use this data to help keep our lake clean and healthy!
This past year we embarked on a project to remotely monitor the water levels on Long Lake. We interviewed several different equipment suppliers and ultimately chose to partner with Stevens Water.  The equipment we chose was physically installed last September 20’. Afterward, the team worked through the winter designing data dashboards and configuring equipment.  We are now pleased to announce the release of the first version of the water monitoring dashboard!

On the dashboard, we show lake levels from both the Long Lake side of the dam and the Fox Lake side. We also added NOAA rainfall data and sensor data from certain locations on the Fox Lake Chain to create a full view of everything we have available to us. It is quite an achievement and we would like to thank Joe, Ryan and Erik for their efforts to make it happen. Please visit the site and feel free to explore.

https://stevens-connect.com/public/project/383/dashboard#profile_id=1033​

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