Where is Randolph Lake?

Randolph Lake is a lake in Randolph County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.

What is the water temperature of Randolph Lake?

Randolph Lake typically sits around 66°F at the surface in October, from 257 EPA Water Quality Portal field readings (2016–2021). That is a typical value for the month, not a live reading.

How deep is Randolph Lake?

No published bathymetric survey covers Randolph Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 34 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.

Can I fish at Randolph Lake?

Public access to Randolph Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Illinois's fish and wildlife agency, so check its current regulations before you go.

Randolph Lake

Randolph County, IllinoisView map Directions

Illinois EPA publishes the water-quality measurements for Randolph Lake. Here is what has been measured.

Clarity

1.7 ft

Typical for Illinois

Secchi · sampled 2021

Phosphorus

87.5 µg/L

Typical for Illinois

Measured by Illinois EPA

Chlorophyll-a

44.9 µg/L

Typical for Illinois

Measured by Illinois EPA

Water temp

~66°F

Typical for Oct · EPA WQP

Max depth

~34 ft est.

GLOBathy model

Type

Hypereutrophic

Trophic class

Hypereutrophic
34 ft max depth
Public access
Limited data

See the measurements Directions Where to stay

Randolph Lake in Randolph County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1.7 ft visibility. Phosphorus: 87.5 µg/L. Chlorophyll-a (algae): 44.9 µg/L.

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Randolph Lake is a highly nutrient-loaded hypereutrophic lake in Randolph County, Illinois with an estimated average depth of about 34 feet. Limited fish-species data available. Public access is available. Compared to the 2 other monitored lakes in Randolph County, Randolph Lake ranks #1 for water quality.

Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2021-10-13. Methodology: how these readings are compared.

Swimming conditions

Readings only

Limited data

Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.

Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.

Whether Randolph Lake is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.

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Water quality measurements for Randolph Lake

These are the measurements Illinois EPA publishes for Randolph Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.

Very murky, less than 1.7 ft of visibility. Phosphorus 87.5 µg/L. Chlorophyll-a 44.9 µg/L. TSI 69.

Water quality readings
Measure	Reading	Where it sits
Water clarity (Secchi depth)	1.7ft	Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer.
Total phosphorus	87.5µg/L	Poor GoodFairPoor
Chlorophyll-a (algae)	44.9µg/L	Poor GoodFairPoor
Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a.	69	Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic

Very high nutrients, dense algae, poor clarity

Ask about Randolph Lake

Answers come straight from the public measurements and survey records on this page.

Water Temperature

Randolph Lake typically sits around 66°F at the surface in October. Summer average is about 71°F. Usually warmest in Jul (about 73°F) and coldest in May (about 61°F). These are typical values by month — not a live reading.

Jan

Feb

Mar

63°

Apr

61°

May

68°

Jun

73°

Jul

Aug

Sep

66°

Oct

Nov

Dec

Column height runs from this lake’s coldest month (61°F) to its warmest (73°F).

Typical surface water temperature by month, from 257 field readings (2016–2021) via the EPA Water Quality Portal. See the full Randolph Lake water temperature breakdown →

Lake Details

Max depth

~34 ft est.

Public access

Yes

Listed by Illinois EPA

Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Randolph Lake.

Lake Size & Watershed

Watershed (drainage) area

7 sq mi

HydroLAKES / HydroSHEDS

Surface area

57 acres

HydroLAKES / HydroSHEDS

Shoreline

2.2 mi

HydroLAKES / HydroSHEDS

Elevation

482 ft

Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.

Stays via Stay22

Stays near Randolph Lake

Compare lakeside cabins, hotels, and vacation rentals near Randolph Lake in Randolph 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Randolph Lake are listed below.

Top-rated places to stay near Randolph Lake

Prices for Oct 23–25, 4 adults. Change dates on the map below.

Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.

Planning a whole trip? See where to stay at Illinois’s top lakes →

Follow Randolph Lake’s readings

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Fishing Randolph Lake

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

Reservoir Info (USACE NID)

Randolph Lake is a man-made reservoir impounded by the Randolph County Lake Dam (completed 1960), built primarily for recreation on the MORRISON BRANCH; earth-type dam, 47 ft tall and 665 ft long.

Normal storage: 946 ac-ft
Max storage: 1,563 ac-ft
Hazard class: Significant
Owner: ILLINOIS DEPARTMENT OF NATURAL RESOURCES

Source: USACE National Inventory of Dams, NID ID IL00551 · Operator website · Matched by proximity (0.44 km)

Nearby Lakes in Randolph County

Randolph County Lake—View →Old City Reservoir—View →Sparta Northwest Lake2.6 ft clear · Hypereutrophic12.1 miView →New City Reservoir—View →West C Streamline Lake—View →Baldwin Lake—View →

Frequently asked questions about Randolph Lake

Where is Randolph Lake?: Randolph Lake is a lake in Randolph County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Randolph Lake?: Randolph Lake in Randolph County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1.7 ft visibility. Phosphorus: 87.5 µg/L. Chlorophyll-a (algae): 44.9 µg/L.
Is Randolph Lake safe to swim in?: Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Randolph Lake?: Randolph Lake typically sits around 66°F at the surface in October, from 257 EPA Water Quality Portal field readings (2016–2021). That is a typical value for the month, not a live reading.
How deep is Randolph Lake?: No published bathymetric survey covers Randolph Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 34 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Can I fish at Randolph Lake?: Public access to Randolph Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Illinois's fish and wildlife agency, so check its current regulations before you go.

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Where this data comes from

52 measurements from 3 monitoring stations, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.

Collected and reported by

illinois epaIL_EPA_WQX52 samples · 2021

Analytical methods

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

Monitoring station identifiers (3)

EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.