Where is Tecumseh Lake?

Tecumseh Lake is a lake in Hardin County, Illinois. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.

What is the water temperature of Tecumseh Lake?

Tecumseh Lake typically sits around 80°F at the surface in August, from 164 EPA Water Quality Portal field readings (2010–2020). That is a typical value for the month, not a live reading.

Tecumseh Lake

Hardin County, Illinois13 acresView map Directions

Nutrient-rich

Nutrients and algae run above the regional average.

↓ down from B at the last regrade

Water temp

~80°F

Typical for Aug · EPA WQP

Clarity

3.6 ft

Secchi · sampled 2020

Level

No gauge

Trend

Not enough history

Eutrophic
#1 of 1 in the county
Limited data

See the measurements Directions Where to stay

Tecumseh Lake in Hardin County, Illinois has a water quality grade of D (Nutrient-rich). Water clarity: 3.6 ft visibility. Phosphorus: 27 µg/L. Chlorophyll-a (algae): 22.5 µg/L. Surface area: 13 acres.

Clarity: 3.6 ft
Typical in August: 80°F
Area: 13 acres
Type: Eutrophic
Phosphorus: 27 µg/L
Chlorophyll-a: 22.5 µg/L

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Stays via Stay22

Stays near Tecumseh Lake

Compare lakeside cabins, hotels, and vacation rentals near Tecumseh Lake in Hardin County, Illinois — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Tecumseh Lake are listed below.

Top-rated places to stay near Tecumseh Lake

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Tecumseh Lake is a 13-acre productive, nutrient-rich eutrophic lake in Hardin County, Illinois. Water quality is graded D based on 2 sampling years through 2020.

Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2020-10-29. Grade methodology: LakeQuality methodology.

Swimming Safety

Grade only

Limited data

Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.

The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.

Get alerts for Tecumseh Lake →

Water Quality Grade: D (Nutrient-rich)

Murky, only visible to about 3.6 ft. Phosphorus 27 µg/L. Chlorophyll-a 22.5 µg/L. TSI 57. The letter is not a swimming clearance.

Metric	Value	Grade
Water Clarity (Secchi Depth)	3.6 ft	Not graded
Phosphorus	27 µg/L	Fair
Chlorophyll-a (Algae)	22.5 µg/L	Poor
Trophic State Index (TSI)	57	Eutrophic

High nutrients, frequent algae, reduced clarity

Water Temperature

Tecumseh Lake typically sits around 80°F at the surface in August. Summer average is about 80°F. Usually warmest in Jul (about 82°F) and coldest in Apr (about 60°F). These are typical values by month — not a live reading.

Jan

—

Feb

—

Mar

—

Apr

60°

May

—

Jun

78°

Jul

82°

Aug

80°

Sep

—

Oct

63°

Nov

—

Dec

—

Typical surface water temperature by month, from 164 field readings (2010–2020) via the EPA Water Quality Portal. See the full Tecumseh Lake water temperature breakdown →

Lake Details

Characteristic	Value
Surface Area	13 acres

No bathymetric survey has been published for Tecumseh Lake, so its depth is not documented here.

Fishing Tecumseh Lake

→ Tecumseh Lake fishing regulations (limits, seasons, special rules)

Reservoir Info (USACE NID)

Tecumseh Lake is a man-made reservoir impounded by the Techumseh (completed 1976), built primarily for recreation on the TR-BIG CREEK; other-type dam, 26 ft tall and 550 ft long.

Surface area: 13 ac
Normal storage: 75 ac-ft
Max storage: 100 ac-ft
Drainage area: 0 sq mi
Hazard class: Low
Owner: USDA FS

Source: USACE National Inventory of Dams, NID ID IL50614 · Operator website · Matched by proximity (0.14 km)

Regulated Pollution Sources Nearby

7 EPA-permitted facilities operate within about 5 miles of Tecumseh Lake under Clean Water Act (NPDES) discharge permits. 4 facilities have a reported Clean Water Act violation in the past three years.

Elizabethtown Stp, Village Of
Elizabethtown · 2.5 mi away · NPDES IL0074250
Recent violation
Responsible Energy Operations Llc
Elizabethtown · 3 mi away · NPDES IL0080095
Recent violation
Hastie Mine
Rosiclare · 3.5 mi away · NPDES IL0073385
Recent violation
Illinois American Water - Rosiclare Stp
Rosiclare · 4.8 mi away · NPDES IL0034207
Recent violation
Elizabethtown, Village Of
Elizabethtown · 2.8 mi away · NPDES IL0028690
Ozark-Mahoning Company
Rosiclare · 4.2 mi away · NPDES IL0032379

Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.

County Ranking

Ranked #1 of 1 lakes in Hardin County

Nearby Lakes in Hardin County

DOne Horse Gap Lake4 ft clear · Eutrophic7 miView →DPounds Hollow Lake3.9 ft clear · Eutrophic9.7 miView →NRMud Lake—View →NRGlen Jones Lake—View →NRSnockey Pond—View →NRBig Lake—View →

Frequently asked questions about Tecumseh Lake

Where is Tecumseh Lake?: Tecumseh Lake is a lake in Hardin County, Illinois. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Tecumseh Lake?: Tecumseh Lake in Hardin County, Illinois has a water quality grade of D (Nutrient-rich). Water clarity: 3.6 ft visibility. Phosphorus: 27 µg/L. Chlorophyll-a (algae): 22.5 µg/L. Surface area: 13 acres.
Is Tecumseh Lake safe to swim in?: The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Tecumseh Lake?: Tecumseh Lake typically sits around 80°F at the surface in August, from 164 EPA Water Quality Portal field readings (2010–2020). That is a typical value for the month, not a live reading.

Explore Tecumseh Lake across LakeQuality

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Species activity outlook by water temperature and season

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Other Grade D Lakes in Illinois

One Horse Gap Lake

Pope County · 4 ft

Pounds Hollow Lake

Gallatin County · 3.9 ft

Vienna Correctional Center Lake

Johnson County · 4.5 ft

Lake of Egypt

Williamson County · 3.2 ft

Wesslyn Cut Lake

Perry County · 4.5 ft

Vernor Lake

Richland County · 4.8 ft

Eutrophic Lakes in Illinois

One Horse Gap Lake Pounds Hollow Lake Vienna Correctional Center Lake Lake of Egypt

Where this data comes from

36 measurements from 2 monitoring stations, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.

Collected and reported by

illinois epaIL_EPA_WQX36 samples · 2020

Analytical methods

MEASURED IN FIELD
Phosphorus by Colorimetry
10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer

Monitoring station identifiers (2)

Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.