How deep is Thomas Lake?

Thomas Lake has a maximum depth of 110 feet. The lake covers 1465.19 acres.

Does Thomas Lake have blue-green algae?

There is no recent EPA CyAN cyanobacteria estimate for Thomas Lake (clouds, ice, or an off-season gap). The most recent reading was high (310,456 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.

Thomas Lake

Not yet rated

14.2 ft clear · Oligotrophic · 1,465 acres

Limited DataOligotrophic

Thomas Lake in Lake County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.2 ft visibility. Maximum depth: 110 ft. Surface area: 1465.19 acres.

Clarity: 14.2 ft
Max depth: 110 ft
Area: 1,465 acres
Trend: → Stable
Public access: No

Where to stay →Safe to swim?

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NRHatchet Lake7 ft clear · Lake CountyView →

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Loading map…

Free interactive depth-contour map of Thomas Lake, reaching a maximum surveyed depth of 110 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.

Why Thomas Lake has no grade

We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Thomas Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).

Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.

Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.

Thomas Lake is a 1,465-acre lake in Lake County, Minnesota with a maximum depth of 110 feet. Limited fish-species data available. No public access — the lake is private or restricted.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-01. Grade methodology: LakeGrade methodology.

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Swimming Safety

Not rated

Limited data

Not rated for swimming — there is not enough monitoring data to judge this lake

Compare the safest swimming lakes near Ely →

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Water quality measurements for Thomas Lake

These readings exist but do not meet the evidence bar for an A–F grade — see why.

Good clarity, visible to about 14.2 ft. Trophic State Index: 39.

Metric	Value	Grade
Water Clarity (Secchi Depth)	14.2 ft	Not graded
Phosphorus	No recent samples
Chlorophyll-a (Algae)	No recent samples
Trophic State Index (TSI)	39	Oligotrophic

Low nutrients, clear water, excellent for swimming

Where to stay near Thomas Lake

Compare lakeside cabins, hotels, and vacation rentals near Thomas Lake in Lake County, Minnesota — 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.

Top-rated places to stay near Thomas Lake

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

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Blue-Green Algae (Cyanobacteria)

No current satellite reading

There’s no recent EPA CyAN cyanobacteria estimate for Thomas Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (310,456 cells/mL) on November 29, 2025.

Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗

Lake Details

Characteristic	Value
Maximum Depth	110 ft
Surface Area	1,465 acres
Shoreline Length	26.2 mi
Littoral Zone	30%
Public Access	No

Lake Size & Watershed

Watershed (drainage) area

182 sq mi

Elevation

1,526 ft

Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).

Fishing Thomas Lake

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

DNR Fisheries Survey Summary

4 surveys on file from MN DNR Fisheries. Most recent: 2025-08-03 (Targeted Survey).

Top Species by Catch Rate

Species	Avg CPUE	Avg Weight
Walleye	8.00	2.25 lb
Tullibee (Cisco)	7.19	0.1 lb
White Sucker	2.05	1.92 lb
Lake Trout	1.60	3.24 lb
Rock Bass	0.75	0.16 lb
Northern Pike	0.69	4.23 lb

CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.

Length Distributions

Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.

Walleye

82 fish · 7–25 in · 2012-09-10

Tullibee (Cisco)

125 fish · 6–10 in · 2012-09-10

White Sucker

28 fish · 8–20 in · 2012-09-10

Lake Trout

15 fish · 10–35 in · 2012-09-10

From the 2025-08-03 survey

Temperature and dissolved oxygen measurements were collected from the deepest basin in Thomas Lake on August 3rd, 2025. This was done to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Lake Trout, the most sensitive coldwater species present in this lake (Cisco, also…

Source: MN DNR LakeFinder Fisheries Lake Survey

DNR Reports & Resources

Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Thomas Lake. 1 report on file.

These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).

—
Fisheries Lake Survey — Thomas
Fisheries Lake Survey · MN DNR LakeFinder

Water Quality Trend: → Stable

Based on 5 years of monitoring data (2020-2025).

Metric	Trend	Change/Year	Years
Water Clarity	→ Stable	+0.013 m/yr	5

See year-by-year chart →

EPA Impairment Status

Thomas Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).

Causes of impairment

Mercury

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit MN38-0351-00 · Official waterbody report

Nearby Lakes in Lake County

NRHatchet Lake7 ft clearView →NRKiana Lake13.8 ft clearView →NRIma Lake11 ft clearView →NRFraser Lake12.5 ft clearView →NRAlice Lake8.2 ft clearView →NRHam Lake6 ft clearView →

Frequently asked questions about Thomas Lake

What is the water quality grade for Thomas Lake?: Thomas Lake in Lake County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 14.2 ft visibility. Maximum depth: 110 ft. Surface area: 1465.19 acres.
Is Thomas Lake safe to swim in?: Not rated for swimming — there is not enough monitoring data to judge this lake. Thomas Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
How deep is Thomas Lake?: Thomas Lake has a maximum depth of 110 feet. The lake covers 1465.19 acres.
Does Thomas Lake have blue-green algae?: There is no recent EPA CyAN cyanobacteria estimate for Thomas Lake (clouds, ice, or an off-season gap). The most recent reading was high (310,456 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.

Explore Thomas Lake across LakeGrade

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Minnesota Fishing Guide

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Where this data comes from

37 measurements from 20 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.

Collected and reported by

Minnesota Pollution Control Agency - Ambient Surface WaterMNPCA37 samples · 2020–2025

Analytical methods

Field measurement/observation, generic method

Monitoring station identifiers (20)

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.

Other records on this page

Impairment status from EPA ATTAINS 303(d) database

Lake size & watershed from HydroLAKES (HydroSHEDS)

Lake details from Minnesota DNR LakeFinder