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Lake Information

County: Fulton

Acreage: 4000

Average Depth: 0.00 feet

Recreational Amenities

Boat Fishing? Electric only

Boat Ramps? Yes

Boat Rental? No

Skiing? No

Swimming? No

Picnicking? Yes

Camping? No

There are no zebra mussels in this lake.

Fish Stocking






Alligator Gar



Additional information for stocking on Thompson Lake - Emiquon

Fishing Outlook  ( Full PDF Report )

Click here for a list of all reports.



Fish Status



In 2022 the bluegill population was sampled by 193 fish by electrofishing. The survey samples represent a bluegill population with a good distribution from .8 to 9.0 inches long. The bluegill recruitment was on the low side again in 2022. The last high recruitment year for bluegill was in 2019. The body condition remained good with an average Wr of 100 for the fish over 5 inches. The bluegill electrofishing collection rate for stock size fish (over 3.1 inches) was 1.4 fish per minute in 2022. This is a decrease from 2.1 fish per minute in 2021 and from the 3.4 fish per minute collected in 2020. This density trend will be evaluated in the future. The bluegill PSD value of 49 for electrofishing was close to the objective range of 20 to 40 in 2022. And it is a reflection of the population being well distributed over the length range. The bluegill RSD7 was at 22 which is just above the objective range of 5 to 20, and near the 5 year average of 26. The RSD8 value of 3 is low and is reflected in the lower numbers of quality bluegill that has existed at Emiquon since 2019. The dense stands of submerged aquatic vegetation is the key to allow the current bluegill population the potential for an excellent spawn and recruitment. These large areas of vegetated habitat would also provide a preferred niche for the Lepomis sp. in competition with the expanding gizzard shad and common carp population. However, these vegetation areas have not been present at high levels in the last 3 years.


Very Good

The bowfin population was sampled by a total of 53 fish from 15.4 to 30.5 inches in 2022. Several year classes appear to be present. The body condition of many of these fish was average to poor in 2022. I have no easy explanation for this, and it will be evaluated going forward. The bowfin population has seen an increase in density and biomass in the sampling over the past 10 years. In 2022 the electrofishing rates were .15 fish per minute. This is consistent with the 5 year average collection rate for the Emiquon Preserve.


Very Good

13 channel catfish were sampled in 2022 by electrofishing and 84 in trapnets. This continues the upward density trend since their consistent sampling that started in 2014. In 2022, the size ranged from 12.2 to 30.8 inches in length. The body condition was only average in 2022 with a Wr value of 88 in the spring and a Wr value of 86 in the fall. If turbid water conditions exist in the future, channel catfish recruitment should continue at a high level. The current channel catfish regulation is a maximum harvest of 6 fish per day per angler. The main scope of this regulation is to prevent wanton waste by anglers.



The black crappie population was sampled by 225 stock sized fish by electrofishing in 2022. The black crappie electrofishing collection rate was 1.9 fish per minute for all sizes in 2022. This rate was above the 5 year average of 1.7 fish per minute of electrofishing. The black crappie sample shows a low number fish in the YOY class from 2.4 to 5.9 inches long and multiple year clasess from 7.9 to 14.0 inches long. The body condition was still a very good Wr of 107 for the fish over 8 inches. The white crappie population was again sampled at a low density at .17 fish per minute. The size range was from 8.7 to 13.0 inches in length. The body condition average was very good at a Wr of 107. This dense crappie population with larger fish present, will feed on the gizzard shad population and also provide additional predation upon potential exotic and invasive fish species reproduction. The future emergence of the white crappie population to a common occurrence will probably depend upon the water clarity. In a lake habitat with both species of crappie, the black crappie tend to dominate in clearer water, while the white crappie tend to succeed with more turbid conditions. The current crappie regulation is a 9 inch minimum size limit and a maximum harvest of 25 fish per day per angler. The goal of this regulation is to maintain a dense crappie population and allow a sustainable high, yearly harvest.



In 2022, the largemouth bass population was sampled by 101 fish by electrofishing. The largemouth bass population was defined by an average year of recruitment with 11 fish sampled from 3.7 to 8.0 inches. The fall 2022 electrofishing survey indicated that the largemouth bass population density has begun to drop. The collection rate of stock size bass (over 8 inches) dropped from 1.4 fish per minute in 2021 at 155 pounds per hour, to .67 fish per minute at 87 pounds per hour in 2022. This was a decline from the 2.5 fish per minute and 246 pounds per hour collected in 2020. The bass population structure is currently skewed high due to the limited number of fish under 12 inches in length. The PSD value of 86 is above the typical objective of a PSD index rating of from 40 to 60. In other words, 86% of the Emiquon bass population was over 12 inches in length. The RSD15 value of 49, RSD18 value of 17 and RSD19 value of 7 were also very high. The body condition rating (Wr) did remain in the good level at an average of 100 in 2022. The previous 5 years had shown a trend of lower body condition values into the 80’s for the bass from 16 to 19 inches. In 2021 and 2022 the largemouth bass data was much improved for this size group of fish. Overall, the largemouth bass population appears to be declining in overall density. The population appears to be in balance with the current forage and water conditions available in the Emiquon Preserve. The main concern will be the need for stronger year class production and recruitment over the next several years. The goal of the initial 18 inch minimum size limit was to create a high density bass population. The predation exerted by this population is necessary to control the exotic and invasive fish reproduction and recruitment that may occur. This predation is also the key to maintain the native species balance within the habitat.



In 2022 the pumpkinseed population was sampled by 16 fish by electrofishing. These fish ranged from 2.4 to 6.5 inches in length. The body condition was a good at an average Wr of 93. The pumpkinseed electrofishing collection rate for stock size fish (over 3.1 inches) was .1 fish per minute. This is an improvement over the last 4 years. Our electrofishing effort in the large rip rap in front of the control gate in the main ditch held all of the fish sampled in 2022. Dense stands of submerged aquatic vegetation will be a key to allow the current pumpkinseed population the potential for an improved spawn and recruitment in the future.



The yellow bass introduction into the Emiquon Preserve has allowed this population to expand rapidly since 2018. The catch per minute rate by electrofishing went up from .49 fish per minute in 2020 to 1.1 fish per minute in 2021. And the corresponding catch rate per trap net night hour went up from 1.1 to 14.5 fish per net night. In 2023, yellow bass from 9 to 11 inches will be very common. From a sportfish management perspective, the large increase in the yellow bass and freshwater drum populations is considered a negative factor for food and space competition for other more important fish species like bluegill, crappie and young largemouth bass.

Location: The Nature Conservancy's Emiquon Preserve is adjacent to the Illinois River in Fulton County, Illinois, approximately 1 mile northwest of Havana and 3 miles southeast of Lewistown.

Description: Historically, what is now the Emiquon Preserve included two backwater lakes, Thompson Lake and Flag Lake, and was argued to have been one of the better hunting and fishing complexes in the Illinois River Valley if not the whole Midwest. From the early 1920s through the present, most of the property currently owned by the Conservancy was managed for agriculture, most recently primarily for intensive row-crop production. In 2007, the site pumps were shut off and the water level in the site was allowed to rise and reform the lakes. The current Thompson/Flag Lake covers approximately 4,000 surface acres. The lake topography is two large shallow basins with deep water ditches dissecting it. In midsummer, the lake basins can be 70% covered with aquatic vegetation.

History and Status of the Sport Fishery: In 2007, The Nature Conservancy entered into a cooperative fish management agreement with the Illinois Department of Natural Resources for the Emiquon Preserve. The water bodies on the site underwent an immediate fish rehabilitation project to remove exotic fish species. The IDNR initiated fish restocking in 2007 with brood fish that included: llargemouth bass, white crappie, black crappie, bluegill, bowfin, spotted gar, channel catfish, brown bullhead, warmouth, orangespotted sunfish, pumpkinseed sunfish, golden shiner, brook silverside, and blackstripe topminnow. IDNR fish stockings and surveys have resulted in the potential of at least 43 fish species now present in the lake.

In 2022, the total exotic fish collected were 79 common carp, 9 silver carp and 3 grass carp.

These new fish species collections probably entered the Preserve from the Illinois River through the new control structure site. The size of these fish indicate that they arrived through a large passage like the control structure. The silver carp, bighead carp and the grass carp had extremely robust body conditions. Their growth rate is currently at an accelerated rate in the Preserve. No reproduction and recruitment has been documented at this time for the Asian carp species.

The presence of an expanding population of common carp, grass carp and silver carp is an ominous sign for the future aquatic habitat in the Preserve. The rapid removal of the submerged aquatic plant community through consumption by the grass carp, and decreased water clarity from algal blooms stimulated by the silver carp biomass may soon reach a critical tipping point. Then the reduced water clarity will likely allow the common carp to achieve very high reproduction and recruitment in the Preserve. A rapid degradation of the aquatic habitat, submerged aquatic plant community, and native fish population is the factual, proven result from a high common carp density.

Additional Lake Information: Public access to the water bodies on the Emiquon Preserve is limited to registered boats. Free annual registration to access the site for all users is required and available at the adjacent Dickson Mounds State Museum. Only electric trolling motors are allowed. No gas motors are allowed on the boats.

2 pole and line fishing only. A concrete boat ramp with a gravel parking lot for 25 vehicle/trailers is present and a boardwalk, visitor area and canoe launch.

The site contains an inviolate refuge from public access. This refuge will attempt to serve as a limited disturbance area for all of the wildlife utilizing the Preserve. This refuge encompasses approximately the eastern half of the former Thompson Lake basin, all of the former Flag Lake basin and then to the Illinois River levee. This refuge area is designated with marked buoys and signs. The access time to the water bodies is sunrise to sunset. This access is year round, except during the Central Zone waterfowl hunting season. During the Central Zone waterfowl hunting season, no water access is allowed on hunting days. Currently waterfowl is allowed 3 days a week, thereby allowing fishing access 4 days a week. Ice fishing is allowed when practical on the entire lake basin.

Site Regulations:

Largemouth Bass: 1 fish daily limit; 18" minimum length limit
Bluegill: 25 fish daily limit; no length limit
Channel Catfish: 6 fish daily limit; no length limit
Walleye, Sauger or Hybrid Walleye: 6 fish daily limit; 14" minimum length limit
White and Black Crappie: 25 fish daily limit; 9" minimum length limit

Contact Information:
The Nature Conservancy Site Office
IDNR Fisheries Biologist, Rob Hilsabeck