Where is Grand Portage Lake?

Grand Portage Lake is a lake in Iron County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.

What is the water temperature of Grand Portage Lake?

Grand Portage Lake typically sits around 73°F at the surface in September, from 16 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.

How deep is Grand Portage Lake?

Grand Portage Lake has a maximum depth of 33 feet. The lake covers 148 acres.

Are there boat ramps on Grand Portage Lake?

Grand Portage Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Grand Portage Lake. Public access is listed as yes.

Can I fish at Grand Portage Lake?

Grand Portage Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Wisconsin's fish and wildlife agency, so check its current regulations before you go.

Grand Portage Lake

Iron County, Wisconsin148 acresView map Directions

Wisconsin DNR publishes the water-quality measurements for Grand Portage Lake. Here is what has been measured.

Clarity

11.7 ft

Typical for Wisconsin

Secchi · sampled 2026

Phosphorus

12.4 µg/L

Less phosphorus than most

Measured by Wisconsin DNR

Water temp

~73°F

Typical for Sep · EPA WQP

Max depth

33 ft

Bathymetric survey

Area

148 acres

Surface area

Type

Mesotrophic

Trophic class

Mesotrophic
33 ft max depth
Public access
Limited data

See the measurements Directions Where to stay

Grand Portage Lake in Iron County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 11.7 ft visibility. Phosphorus: 12.4 µg/L. Maximum depth: 33 ft. Surface area: 148 acres.

Wisconsin DNR lists Musky as common on Grand Portage Lake. DNR survey details →

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Grand Portage Lake is a 148-acre mesotrophic lake in Iron County, Wisconsin with a maximum depth of 33 feet. Overall water quality is improving over recent sampling years. The lake supports 6 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 1 public boat landing. Compared to the 15 other monitored lakes in Iron County, Grand Portage Lake ranks #12 for water quality.

Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-09. Methodology: how these readings are compared.

Grand Portage Lake covers about 150 acres in Iron County. It has one public boat landing. If you are planning to stay, you can search lake houses and cabins around Grand Portage Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.

What Grand Portage Lake is good for

From access and monitoring records, not editorial picks.

Clear water11.7 ft of visibility
Boat launch1 documented ramp
Fishing6 species recorded
Deep water33 ft surveyed max depth

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 Grand Portage Lake is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.

Compare swimming lakes near Minocqua →

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Water quality measurements for Grand Portage Lake

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

Good clarity, visible to about 11.7 ft. Phosphorus 12.4 µg/L. TSI 41.

Water quality readings
Measure	Reading	Where it sits
Water clarity (Secchi depth)	11.7ft	Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer.
Total phosphorus	12.4µg/L	Good GoodFairPoor
Chlorophyll-a (algae)		No reading The green pigment in algae — a direct measure of how much algae is in the water.
Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a.	41	Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic

Moderate nutrients, good water quality

Ask about Grand Portage Lake

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

Water Temperature

Grand Portage Lake typically sits around 73°F at the surface in September. Summer average is about 74°F. Usually warmest in Jul (about 76°F) and coldest in Apr (about 49°F). These are typical values by month — not a live reading.

Jan

Feb

Mar

49°

Apr

59°

May

75°

Jun

76°

Jul

72°

Aug

73°

Sep

Oct

Nov

Dec

Column height runs from this lake’s coldest month (49°F) to its warmest (76°F).

Typical surface water temperature by month, from 16 field readings (2024–2025) via the EPA Water Quality Portal. See the full Grand Portage Lake water temperature breakdown →

DNR fisheries survey

Wisconsin DNR lists Musky as common on Grand Portage Lake.

A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Grand Portage Lake’s water-quality measurements separately, and the water-quality trend over 7 years of monitoring is improving. 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 2009. 2 stations on file (most recent sample 2025).

DNR Assessment

Excellent · Deep Lowland lake

Trophic State Index 42 (mesotrophic) · 5-year average

Fish Species (DNR-rated)

Musky(Common)Panfish(Common)Largemouth Bass(Common)Northern Pike(Common)Walleye(Common)Smallmouth Bass(Present)

Contour map (PDF) →Full WI DNR LakePage →Water quality stations →

Lake Details

Max depth

33 ft

Surface area

148 acres

Public access

Yes

Listed by Wisconsin DNR

Lake Size & Watershed

Watershed (drainage) area

86 sq mi

HydroLAKES / HydroSHEDS

Shoreline

3 mi

HydroLAKES / HydroSHEDS

Elevation

1,585 ft

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

Recreation & Access

Boat Landings

Yes

Public Access

Grand Portage LakePublic

Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps

Stays via Stay22

Stays near Grand Portage Lake

Compare lakeside cabins, hotels, and vacation rentals near Grand Portage Lake in Iron 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 Grand Portage Lake

Prices for Oct 9–11, 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 Wisconsin’s top lakes →

Follow Grand Portage Lake’s readings

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Fish Species

Musky Panfish Largemouth Bass Smallmouth Bass Northern Pike Walleye

Click a species to see every lake where it is documented.

Fishing Grand Portage 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.

Banded Mystery SnailEurasian Water-Milfoil

Water Quality Trend: Improving

Based on 7 years of monitoring (2020–2026).

Water clarity
Stable
6 years
Phosphorus
Improving
-1.12 µg/L/yr7 years

See year-by-year chart →

Nearby Lakes in Iron County

San Domingo Lake—View →Echo Lake6 ft clear · Mesotrophic—View →Echo Lake—View →Mercer Lake12 ft clear · Mesotrophic—View →Martha Lake9 ft clear—View →Little Martha Lake—View →

Frequently asked questions about Grand Portage Lake

Where is Grand Portage Lake?: Grand Portage Lake is a lake in Iron County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Grand Portage Lake?: Grand Portage Lake in Iron County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 11.7 ft visibility. Phosphorus: 12.4 µg/L. Maximum depth: 33 ft. Surface area: 148 acres.
Is Grand Portage 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 Grand Portage Lake?: Grand Portage Lake typically sits around 73°F at the surface in September, from 16 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Grand Portage Lake?: Grand Portage Lake has a maximum depth of 33 feet. The lake covers 148 acres.
What fish are in Grand Portage Lake?: Fish species found in Grand Portage Lake include Musky, Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Grand Portage Lake is located in Iron County, Wisconsin.
What did the DNR fisheries survey find at Grand Portage Lake?: Wisconsin DNR lists Musky as common on Grand Portage Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Grand Portage Lake’s water-quality measurements separately, and the water-quality trend over 7 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Are there boat ramps on Grand Portage Lake?: Grand Portage Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Grand Portage Lake. Public access is listed as yes.
Can I fish at Grand Portage Lake?: Grand Portage Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Wisconsin's fish and wildlife agency, so check its current regulations before you go.

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Where this data comes from

38 measurements from 1 monitoring station, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.

Collected and reported by

Wisconsin Department of Natural ResourcesWIDNR_WQX38 samples · 2020–2026

Analytical methods

Phosphorus by Colorimetry

Monitoring station identifiers (1)

WIDNR_WQX-263138

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.

Other records on this page

Lake size & watershed from HydroLAKES (HydroSHEDS)

Fish and recreation data from Wisconsin DNR Lakes

Named boat-access points from the USGS National Boat Ramps inventory