Portage Lake
Portage Lake in Cook County, Minnesota has a water quality grade of A (Excellent). Water clarity: 8.5 ft visibility. Phosphorus: 9.5 µg/L. Chlorophyll-a (algae): 3.3 µg/L. Maximum depth: 55 ft. Surface area: 128.12 acres.
Minnesota DNR surveys at Portage Lake average 16.44 white sucker per unit of sampling effort (CPUE) across 9 surveys. The most recent is a Standard Survey dated June 8, 2022. Length samples in the latest survey that recorded them ran 6–15 inches. DNR survey details →
- Clarity
- 8.5 ft
- Typical in August
- 57°F
- Max depth
- 55 ft
- Area
- 128 acres
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- No
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Portage Lake is a 128-acre mesotrophic lake in Cook County, Minnesota with a maximum depth of 55 feet (18-foot average). Water quality is graded A based on 2 sampling years through 2020. Overall water quality is declining over recent sampling years. The lake supports 3 documented fish species including green sunfish, splake, and white sucker. No public access — the lake is private or restricted. Compared to the 43 other monitored lakes in Cook County, Portage Lake ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2020-09-15. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 8.5 ft. Phosphorus level: 9.5 µg/L. Chlorophyll-a: 3.3 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.5 ft | Not graded |
| Phosphorus | 9.5 µg/L | Good |
| Chlorophyll-a (Algae) | 3.3 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Portage Lake
Compare lakeside cabins, hotels, and vacation rentals near Portage Lake in Cook 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.
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Water Temperature
Portage Lake typically sits around 57°F at the surface in August. Summer average is about 57°F. Usually warmest in Jun (about 59°F) and coldest in Sep (about 53°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 95 field readings (2018–2019) via the EPA Water Quality Portal. See the full Portage Lake water temperature breakdown →
Minnesota DNR surveys at Portage Lake average 16.44 white sucker per unit of sampling effort (CPUE) across 9 surveys. The most recent is a Standard Survey dated June 8, 2022. Length samples in the latest survey that recorded them ran 6–15 inches.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Portage Lake A from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
9 surveys on file from MN DNR Fisheries. Most recent: 2022-06-08 (Standard Survey).
Top Species by Catch Rate
| Species | Avg catch rate (CPUE) | Avg Weight |
|---|---|---|
| White Sucker | 16.44 | 0.71 lb |
| Fathead Minnow | 3.50 | — |
| Green Sunfish | 2.83 | 0.08 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE means more abundant in standardized sampling. This is not a weekly bite report.
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.
White Sucker
Green Sunfish
From the 2022-06-08 survey
Portage Lake is a designated stream trout lake that has been managed for Splake since 1982. The lake is located near the mid-Gunflint Trail area, about 35 miles from the City of Grand Marais. The most direct public access to the lake is from a 0.10-mile portage trail from the east end of Iron Lake which connects with…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Portage Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — PortageFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — PortageFish Stocking History · MN DNR LakeFinder
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 55 ft |
| Average Depth | 17.8 ft |
| Surface Area | 128 acres |
| Shoreline Length | 6.3 mi |
| Littoral Zone | 60% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Portage Lake
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.503 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.71 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.56 µg/L/yr | 6 |
EPA Impairment Status
Portage Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN16-0342-00 · Official waterbody report · Matched by proximity (0.92 km)
County Ranking
Ranked #7 of 44 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Portage Lake
Where is Portage Lake?
- Portage Lake is a lake in Cook County, Minnesota. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Portage Lake?
- Portage Lake in Cook County, Minnesota has a water quality grade of A (Excellent). Water clarity: 8.5 ft visibility. Phosphorus: 9.5 µg/L. Chlorophyll-a (algae): 3.3 µg/L. Maximum depth: 55 ft. Surface area: 128.12 acres.
Is Portage Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Portage Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 3.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Portage Lake?
- Portage Lake typically sits around 57°F at the surface in August, from 95 EPA Water Quality Portal field readings (2018–2019). That is a typical value for the month, not a live reading.
How deep is Portage Lake?
- Portage Lake has a maximum depth of 55 feet and an average depth of 17.8 feet. The lake covers 128.12 acres.
What fish are in Portage Lake?
- Fish species found in Portage Lake include green sunfish, splake, white sucker. Portage Lake is located in Cook County, Minnesota.
What did the DNR fisheries survey find at Portage Lake?
- Minnesota DNR surveys at Portage Lake average 16.44 white sucker per unit of sampling effort (CPUE) across 9 surveys. The most recent is a Standard Survey dated June 8, 2022. Length samples in the latest survey that recorded them ran 6–15 inches. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Portage Lake A from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Explore Portage Lake across LakeQuality
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Where this data comes from
12 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA12 samples · 2020
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder