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Stratton Lock and Dam

Public Information for Stratton and Algonquin Dams

The Stratton Lock is closed for the winter season each year from Nov. 1 through April 30. 

Stratton Dam Winter Drawdown starts on Nov 1 and continues to Dec 1 of each year. Normal drawdown is 1.26 feet below the crest of the spillway (736.76 ft) to an elevation of 735.5 at Stratton Dam. The resulting drawdown in the lakes is normally about 18 inches as monitored at the lake stations with the lowest drawdown to be 735.5. The winter drawdown gives an additional 14,400 acre-feet of storage for flood control in the Chain-O-Lakes as measured from a summer pool stage of 4.2 feet to a winter drawdown stage of 2.5 feet.  


The Illinois Department of Natural Resources (IDNR) today announced the operating schedule for the William G. Stratton-Thomas A. Bolger Lock and Dam facility on the Fox River in McHenry County, which opens for the 2023 season on Monday, May 1. 

Normal operating hours will be seven days per week from 8:00 a.m. until midnight during the months of May through September, and 8:00 a.m. until 8:00 p.m. for the month of October.

The Stratton-Bolger facility is closed for the winter season each year from November 1 through April 30.  

Stratton Lock and Dam serves as the passageway between the Fox Chain of Lakes in northern Illinois, and the Fox River.

An average of 17,000 boats pass through the aging locks annually, along with millions of gallons of water.

The Office of Water Resources began updating the Operating Guide for Stratton and Algonquin Dams in order to take advantage of additional years of data, in order to better regulate the flow of water downstream to minimize flooding of the residences and communities along the edges of both the Lakes and the river. The Guide continues to be updated and revised, and determines the depth of the winter drawdown and summer pool.

The Operation Guide for the gates at Stratton and Algonquin Dams was developed by studying historic storm events to determine the maximum benefits of the gates on the Fox River region. This analysis included the hinged crest gates before they were constructed. The following narrative describes the dam facilities and the factors effecting gate operations.

The Illinois Department of Natural Resources (IDNR) announced August 19th, 2014, that construction will begin on a $16.7 million improvement project at the Stratton Lock and Dam on the Fox River in McHenry County.

The Stratton Lock and Dam Life Extension Project will improve three components of the lock and dam facility. A new structure will be built upstream and replace the existing gates. The boat lock will be extended in the downstream direction on the river, which will double the current capacity of the lock. Finally, the berm on the west side of the Fox River will be rehabilitated to correct erosion problems.

Construction will not interrupt normal lock usage or water level control. More than 24,000 boats pass through the Stratton boat lock annually.

The existing Stratton Dam gates, which were built in 1939, will remain operational while the new gates are constructed. The new gates were sized to match the capacity of current gates. The project will have no impact on flooding along the Fox River Once the new gates are fully operational, the existing gate structure will be removed.

The Stratton boat lock was constructed in 1960. The lock extension will reduce wait times during high boat traffic periods. The lock mechanical system will be rehabilitated during the construction project. Lock construction will take place during the non-boating season, November 1 thru April 30. The Stratton lock will remain operational during the boating season, May 1 thru October 31. During the peak boating season from May 1 through September 30 the lock is open 8AM to Midnight. In October the lock is open from 8AM to 8PM and is closed for the winter November through April.

As construction begins, the Stratton Lock and Dam will not be open to visitors. Boaters should be alert to the construction exclusion zones near the lock and dam to ensure the safety of boaters and construction crews. Limited fishing access will remain outside the construction fencing.

Kiewit Infrastructure Company of Chicago will complete the construction under the supervision of the IDNR Office of Water Resources. Funding for the project is through capital funds available for dam safety and improvement projects. It is expected that the project should be completed by November 2016.

Fox River Watershed

The Fox River watershed starts in Waukesha County, Wisconsin. Flows rise on the Fox River because a portion of the rainfall falling on the entire watershed flows overland to a stream and eventually enters the Fox River. As it enters Illinois, the Fox River drains 880 square miles from Wisconsin. The largest tributary to the Fox River is Nippersink Creek which enters the Fox River in Pistakee Lake. The Nippersink Creek watershed area is 200 square miles. The Fox River watershed area at Stratton Dam is 1250 squares miles; at Algonquin Dam it is 1400 square miles; and at Montgomery Dam it is 1732 square miles.

Stream gages are used to monitor stream flows throughout the watershed. The gages are operated by the US Geological Survey and reported on the internet in near real time. Several tributaries and the Fox River are monitored. Fox River stream gages are located in Wisconsin at Waukesha, Burlington, and New Munster and in Illinois at Algonquin, Montgomery and Dayton. There are additional gages on the Chain of Lakes and the Fox River at Johnsburg, McHenry Dam, and South Elgin Dam which report river stage only.

Normal Flow Operations

During normal flow operations, 400 cfs to 1800 cfs, the flows that enter the Chain of Lakes are released at Stratton. The Chain of Lakes elevation is maintained at normal pool (summer at stage of 4.2 on Fox Lake or winter at stage of 2.5 on Fox Lake). If the pool elevation needs to be adjusted, more flow is released if the pool is too high and less flow is released if the pool is too low.

Winter Operations

Winter drawdown lowers the Chain of Lakes 1.5' to increase the storage by 10,000 acre-feet, almost doubling the storage. Drawdown begins on November 1 and is targeted to be complete by December 1. The lower levels in the Chain need to be reached before an ice cover is formed. This storage is used as warm weather melts the snow and spring rainfall causes higher flows. The Chain of Lakes rises in the spring when the flows increase. To prevent ice jam flooding, flows at Stratton Dam are limited to 1000 cfs after 60 degree freezing days are reached. Limiting flows may require the use of the storage created by winter drawdown.

Flood Operations

Flood operations begin when predicted peak inflows to the Chain of Lakes exceed 1800 cfs. Gate operations are determined using:

  • Inflows to the Chain of Lakes as monitored at the stream gages at Fox River near New Munster, Wisconsin and Nippersink Creek near Spring Grove, Illinois stage of Fox Lake; and predicted peak inflows to Chain.
  • Gates are opened to achieve a specified flow per the operation guide (Operations of Stratton and Algonquin Dams, Fox River in Lake and McHenry Counties). These flows were determined based on analysis of prior storm events and the impacts to the Fox River and Chain of Lakes.

Estimating Peak Flows using Hydrologic Modeling

Rainfall data is gathered throughout the watershed in Wisconsin and Illinois. The majority of the rainfall data comes from observers who report measured rainfall over the previous 24 hour period to the National Weather Service. The NWS makes this information available around 8:30 every morning. The US Geological Survey operates four near real time precipitation gages. Data is posted on the internet usually within 2 hours. A map (PDF) showing locations where precipitation are recorded is attached.

The rainfall data from the watershed is utilized in hydrologic modeling for the Fox River. The precipitation data is entered into the Fox River Operations Hydrologic Model. The hydrologic modeling computes estimates of peak inflows to the Chain of Lakes. The estimated peak inflows to the Chain of Lakes are used with the current stage of Fox Lake to determine the gate flows from Stratton Dam. The National Weather Service makes the official flood predictions at the Fox River at New Munster, Wisconsin and the Fox River at Algonquin, Illinois utilizing their own hydrologic modeling. The NWS prediction is compared with the OWR estimate to investigate the benefits and impacts of alternative gate operations.

Operation Guide Development

The operation guide criteria for operating the gates were developed with the Illinois State Water Survey. The ISWS developed the hydrologic model. The hydrologic model was calibrated and was utilized with the hydraulic model, Full Equations (FEQ). The hydraulic model was calibrated then verified by the U.S. Geological Survey by making flow measurements and taking water surface elevations during a high water event. These models were used to investigate 10 alternative gate operation scenarios including the use of the proposed hinged crest gates and analyze winter drawdown. The analysis was based on historic storm events. After verifying the benefits of the proposed hinged crest gates, the ISWS developed the refined operation flow chart utilizing predicted peak inflows. This analysis included the hinged crest gates even though the gates were not in place at the time of the analysis.

Storage in Chain of Lakes

The Chain of Lakes is a natural storage area for the Fox River. As flows increase, the Chain of Lakes rises. During a flood event, not all the flow can be released back into the Fox River at Johnsburg since the Fox River is narrower than the Chain of Lakes. During small flood events, the storage in the Chain of Lakes allows for flow management so the flows on the Fox River can be contained in bank. For these small floods, the Chain of Lakes is not allowed to rise so high that flooding occurs. During large flood events, peak inflows above 5000 cfs, the gates at Stratton Dam and Algonquin Dam are open completely. During large flood events the constraints on the flow capacity out of the Chain of Lakes is the channel geometry and not the setting of the gates at Stratton and Algonquin Dams.

Example - June 2008 Event

Most of the flood events are a culmination of several rainfall events in a 10 day period. For example, the June 2008 flooding occurred after rainfall from June 5 thru June 10 (PDF) . The largest amounts of rainfall were recorded on the mornings of June 6, 8 and 9. Flows on Nippersink Creek (PDF) near Spring Grove peaked on June 10. Flows on the Fox River near New Munster (PDF) , Wisconsin peaked on June 15. The highest water surface elevation on Fox Lake was reached on June 18. The gates were opened incrementally based on project peak inflows. The gates were opened on June 6, opened further on June 8, and opened completely on June 9. The criteria (projected peak inflows and Fox Lake stage) to completely open the gates were not reached until after the rainfall on June 8. Note that the gates at both dams were opened completely 9 days before the peak water surface elevation was reached in the Chain of Lakes and 6 days before the peak flows on the Fox River at New Munster.

Using Forecasted Rainfall for Operation Decisions

The ISWS analysis does not recommended using predicted rainfall. Rainfall, especially in the Wisconsin portion of the watershed, takes 1 to 6 days before the runoff enters the Chain of Lakes. Therefore, adequate time exists to open the gates using the recorded rainfall. The Quantitative Precipitation Forecast (QPF), prepared by the NWS, typically over-estimates watershed average rainfall. The largest problem with using the QPF occurs if gates are raised to increase flows above bankfull, i.e. flooding occurs downstream of Stratton Dam based on predicted rainfall.

However, the impacts of predicted rainfall are analyzed. Minor changes to gate settings that may be beneficial if the predicted rainfall occurs may be made if these changes will not induce or increase flooding on residences downstream. The gates will not be opened fully unless flooding throughout the entire Fox River and Chain of Lakes is anticipated.

Benefits of the Hinged Crest Gates

When the hinged crest gates were studied, the analysis showed that the operation of gates would reduce flooding but not eliminate flooding. The ISWS study of alternative operation scenarios showed the use of the hinged crest gates reduced peak water surfaces from the Chain of Lakes to Fox River at Johnsburg by 0.1' to 0.5' during the historic storms. At Stratton Dam the hinged crest gates reduce water surfaces 0.1' to 1.0' for the historic flood events. The hinged crest gate at Algonquin Dam reduces peak water surface elevations immediately upstream of the dam 0.3' to 1.0' for the historic storms. The benefits of the Algonquin hinged crest diminish as you move further upstream. The reduction in peak water surface elevations and flooding justified the economics for construction of the gates.

The maximum potential reduction in water surface elevations during a flood event can be analyzed by removing the dam. The ISWS alternative analysis showed that removal of Stratton dam would reduce water surface elevations upstream of the Stratton dam from 0.25' to 0.5' at extremely large flood events and would have no benefits to the Fox River downstream of Stratton Dam. Removal of Stratton Dam would not eliminate flooding. However, removal of the dam would reduce the recreation opportunities in the Chain of Lakes and Fox River upstream of Stratton Dam.

Information during High Water Events

During flood events, the County Emergency Managers and Stormwater Managers are contacted with daily updates of gate settings and flow at Stratton and Algonquin Dams. The National Weather Service predictions for flows and potential qualitative impacts for the Fox River and Chain of Lakes in Illinois are discussed. This information should be available late morning after decisions for gate operations are made. Gate settings are not available on the internet.

Boating Restrictions

The Fox Waterway Agency has the authority to enact no-wake boating restrictions during high water events. Chapter 5 (PDF) of the FWA ordinance specifies the water stages when these restrictions can be enacted. The Illinois Department of Natural Resources does not have authority to implement no-wake restrictions.

The Illinois Department of Natural Resources can designate a body of water a "Restricted Boating Area" when conditions make navigation of a body of water significantly dangerous to the public. Title 17 Illinois Administrative Code Section 2030.80 describes the procedure for enacting and rescinding a Restricted Boating Area. The determination to enact and rescind a boating restriction is made on a case by case basis. This determination is made based on the totality of circumstances. Section 2030.15 (c) specifies that restricting boating for the purposes of protecting property is prohibited. The Office of Law Enforcement administers Restricted Boating Areas.

Dam Features

Stratton Dam

  • Spillway Crest - 221' long at elevation 736.7
  • Hinged Crest Gate - 50' long with variable height from 6" above spillway (737.2) to 730.3; installed in 2002; status given in feet below the spillway crest
  • Sluice Gates - 5 Gates that are 13.75' long; sill elevation at 731.15 and open 9' (well above water surface); status given in opening height in feet above the sill until maximum opening: out of water
  • Lock - navigational structure to lift or lower boats; not used to move water

Algonquin Dam

  • Spillway Crest - 242' long at elevation 730.3
  • Hinged Crest Gate - 50' long with variable height from 6" above spillway (730.8) to 724.3; installed in 2002; status given in feet below the spillway crest

Gate Operations

Gates are operated by Illinois Department of Natural Resources, Office of Water Resources. Gate Operations fall into 3 categories: low flows, normal flows, and flood flows. Gate operations are determined by:

  • inflows to the Chain of Lakes as monitored at the stream gages at Fox River near New Munster, Wisconsin and Nippersink Creek near Spring Grove, Illinois;

  • stage of Fox Lake; and

  • predicted peak inflows to the Chain of Lakes based on hydrologic modeling from observed precipitation.

Operation Goals

  • maintain a recreational pool,

  • utilize available storage in the Chain of Lakes to minimize regional flooding,

  • maintain minimum flows for water supply and aquatic habitat, and

  • limit flows during ice jam periods.