Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water

Lake County Lake Quality

Illinois, 65 lakes, average grade C (Fair)

Lake County has 65 monitored lakes, enough that within-county variation matters as much as the county average. Some are deep glacial basins, others are shallow agricultural-watershed waters, and the measurements reflect that mix. 19 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.

The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Grays Lake (A); the most-stressed is Long Lake (F).

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Quick Answers for Lake County

Cleanest lakes in Lake County →Cleanest lakes in Illinois →Safest swimming lakes in Illinois →

Planning a trip? Check special fishing regulations for Grays Lake — or check the official Illinois fishing regulations.

All Lakes in Lake County

65 lakes · 19 graded, 46 not rated19 graded lakes · 46 not rated, hidden

Include not-rated lakes (46)

#	Lake	Grade	Clarity	Phosphorus	Algae	Trophic	Access
1	AGrays LakeLake	A	3.5 ft	23 µg/L	3.1 µg/L	No recent samples	Not recorded
2	ACatherine LakeLake	A	7.4 ft	30 µg/L	4.9 µg/L	No recent samples	✓ Public
3	ACedar LakeLake	A	No recent samples	No recent samples	4.7 µg/L	No recent samples	Not recorded
4	ADeep LakeLake	A	No recent samples	No recent samples	2.2 µg/L	No recent samples	Not recorded
5	BRound LakeLake	B	7.4 ft	20.5 µg/L	7.1 µg/L	No recent samples	✓ Public
6	BChannel LakeLake	B	8 ft	36 µg/L	9.5 µg/L	No recent samples	✓ Public
7	BZurich LakeLake	B	No recent samples	No recent samples	7.9 µg/L	No recent samples	Not recorded
8	BWest Loon LakeLake	B	No recent samples	No recent samples	9.3 µg/L	No recent samples	Not recorded
9	CTower LakeLake	C	No recent samples	No recent samples	18.3 µg/L	No recent samples	Not recorded
10	CEast Loon LakeLake	C	No recent samples	No recent samples	15.9 µg/L	No recent samples	Not recorded
11	DFox LakeLake	D	1.9 ft	72 µg/L	28.2 µg/L	No recent samples	Not recorded
12	FLong LakeLake	F	3.4 ft	81 µg/L	57.1 µg/L	No recent samples	✓ Public
13	FGrass LakeLake	F	1.4 ft	103.5 µg/L	37.1 µg/L	No recent samples	✓ Public
14	FMarie LakeLake	F	2.7 ft	76 µg/L	55 µg/L	No recent samples	Not recorded
15	FNippersink LakeLake	F	1.3 ft	88 µg/L	36.6 µg/L	No recent samples	✓ Public
16	FDiamond LakeLake	F	No recent samples	No recent samples	63.6 µg/L	No recent samples	✓ Public
17	FValley LakeLake	F	No recent samples	No recent samples	50.7 µg/L	No recent samples	Not recorded
18	FLouise LakeLake	F	No recent samples	No recent samples	80.2 µg/L	No recent samples	Not recorded
19	FSlocum LakeLake	F	No recent samples	No recent samples	90.3 µg/L	No recent samples	Not recorded
	NRLoch Lomond LakeLake	NR	16.5 ft	No recent samples	No recent samples	No recent samples	✓ Public
	NRHastings LakeLake	NR	3.4 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRTimber LakeLake	NR	10.6 ft	No recent samples	No recent samples	No recent samples	✓ Public
	NRPetite LakeLake	NR	2.5 ft	70 µg/L	59 µg/L	No recent samples	Not recorded
	NRBluff LakeLake	NR	4 ft	315.5 µg/L	30.8 µg/L	No recent samples	✓ Public
	NRSterling LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRMinear LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLiberty LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake CharlesLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSaint Marys LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRGages LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRThird LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDruce LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHighland LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCountryside LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSylvan LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDavis LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake ShereeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBangs LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRWooster LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDuck LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRRedhead LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBrandenburg LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFish LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSullivan LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRGrassy LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake BarringtonLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHoney LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRForest LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRTurner LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRDunns LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSpring LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRAntioch LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCrooked LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSand LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSlough LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMiltmore LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFourth LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake LindenLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWaterford LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRElmwood Farms LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHuntley LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWhite LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSilver LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRRedwing Slough LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDeer LakeLake	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded

NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

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Other Counties in Illinois

Winnebago County

7 lakes · Avg grade A

DeKalb County

1 lake · Avg grade B

Kane County

3 lakes · Avg grade B

Perry County

7 lakes · Avg grade C

Rock Island County

3 lakes · Avg grade C

Jackson County

14 lakes · Avg grade C

See how Lake County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..

Source: EPA National Aquatic Resource Surveys, 2026.