Thomas Lake
Thomas Lake in Portage County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13 ft visibility. Maximum depth: 28 ft. Surface area: 32 acres.
Wisconsin DNR lists Panfish as common on Thomas Lake. DNR survey details →
- Clarity
- 13 ft
- Typical in August
- 73°F
- Max depth
- 28 ft
- Area
- 32 acres
- Trend
- ↓ Declining
- Public access
- Yes
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Why Thomas Lake has no grade
We grade a lake only when the monitoring record supports a letter: 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 WI DNR and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Thomas Lake is a 32-acre lake in Portage County, Wisconsin with a maximum depth of 28 feet. Overall water quality is declining over recent sampling years. The lake supports 4 documented fish species including Panfish, Largemouth Bass, and Northern Pike. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-18. Grade methodology: LakeQuality methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Thomas Lake
These readings exist but are not enough for an A–F grade — see why.
Good clarity, visible to about 13 ft. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Thomas Lake
Compare lakeside cabins, hotels, and vacation rentals near Thomas Lake in Portage County, Wisconsin — 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
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Thomas Lake typically sits around 73°F at the surface in August. Summer average is about 77°F. Usually warmest in Jul (about 80°F) and coldest in Apr (about 49°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 21 field readings (2025–2026) via the EPA Water Quality Portal. See the full Thomas Lake water temperature breakdown →
Wisconsin DNR lists Panfish as common on Thomas Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality does not assign an A–F grade on Thomas Lake — official chemistry is on file, not a letter, and the water-quality trend over 2 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2013. 1 station on file (most recent sample 2026).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Thomas Lake covering fish populations, stocking, water quality, and management. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 2025Thomas Lake spring shocking, 2025Spring Shocking Survey · WI DNR · 2025 (PDF)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 28 ft |
| Surface Area | 32 acres |
| Public Access | Yes |
Recreation & Access
- Thomas LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Thomas Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -3 m/yr | 2 |
Graded lakes near Thomas Lake
Thomas Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Portage County
Frequently asked questions about Thomas Lake
Where is Thomas Lake?
- Thomas Lake is a lake in Portage County, Wisconsin. LakeQuality has not rated this lake (UNRATED) — there is not enough recent sampling to assign a letter.
What is the water quality grade for Thomas Lake?
- Thomas Lake in Portage County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13 ft visibility. Maximum depth: 28 ft. Surface area: 32 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.
What is the water temperature of Thomas Lake?
- Thomas Lake typically sits around 73°F at the surface in August, from 21 EPA Water Quality Portal field readings (2025–2026). That is a typical value for the month, not a live reading.
How deep is Thomas Lake?
- Thomas Lake has a maximum depth of 28 feet. The lake covers 32 acres.
What fish are in Thomas Lake?
- Fish species found in Thomas Lake include Panfish, Largemouth Bass, Northern Pike, Trout. Thomas Lake is located in Portage County, Wisconsin.
What did the DNR fisheries survey find at Thomas Lake?
- Wisconsin DNR lists Panfish as common on Thomas Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality does not assign an A–F grade on Thomas Lake — official chemistry is on file, not a letter, and the water-quality trend over 2 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Are there boat ramps on Thomas Lake?
- Thomas Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Thomas Lake. Public access is listed as yes.
Explore Thomas Lake across LakeQuality
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Where this data comes from
7 measurements from 1 monitoring station, 2025–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX7 samples · 2025–2026
Monitoring station identifiers (1)
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
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory