Portage Lake
Portage Lake in Aitkin County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.5 ft visibility. Maximum depth: 18 ft. Surface area: 372.44 acres.
- Clarity
- 4.5 ft
- Typical in August
- 72°F
- Max depth
- 18 ft
- Area
- 372 acres
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Aitkin County
Why Portage 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 Portage 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.
Portage Lake is a 372-acre lake in Aitkin County, Minnesota with a maximum depth of 18 feet (8-foot average). Overall water quality is declining over recent sampling years. The lake supports 11 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2022-08-07. Grade methodology: LakeGrade 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 Portage Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Murky, only visible to about 4.5 ft. Trophic State Index: 55.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 55 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Portage Lake
Compare lakeside cabins, hotels, and vacation rentals near Portage Lake in Aitkin 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 Portage Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Portage Lake typically sits around 72°F at the surface in August. Summer average is about 71°F. Usually warmest in Jul (about 73°F) and coldest in May (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 43 field readings (2016–2017) via the EPA Water Quality Portal. See the full Portage Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Portage Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (293,765 cells/mL) on May 23, 2026.
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 | 18 ft |
| Average Depth | 8 ft |
| Surface Area | 372 acres |
| Shoreline Length | 5.1 mi |
| Littoral Zone | 84% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Portage LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Portage Lake
DNR Fisheries Survey Summary
10 surveys on file from MN DNR Fisheries. Most recent: 2025-05-14 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 24.14 | 0.22 lb |
| Black Bullhead | 22.38 | 0.43 lb |
| CRP | 17.54 | 0.21 lb |
| Yellow Perch | 11.00 | 0.1 lb |
| Black Crappie | 9.91 | 0.17 lb |
| GOS | 7.71 | 0.12 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.
Bluegill
Black Bullhead
Yellow Perch
Black Crappie
From the 2025-05-14 survey
Portage Lake is 372 acres with an average depth of 8 feet and a maximum depth of 18 feet. A targeted panfish assessment was conducted on 5/14/2025. A total of 34 Bluegill were captured for a trap net catch rate of 5.7 per net. Bluegill averaged 6.7 inches with fish up to 9.3 inches observed. Fish ranged from 2 to 8…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Portage Lake. 3 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
- —Aquatic Plant Report — Portage (0077)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — PortagePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.23 m/yr | 3 |
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 MN01-0069-00 · Official waterbody report
Nearby Lakes in Aitkin County
Frequently asked questions about Portage Lake
What is the water quality grade for Portage Lake?
- Portage Lake in Aitkin County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.5 ft visibility. Maximum depth: 18 ft. Surface area: 372.44 acres.
Is Portage Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Portage 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 Portage Lake?
- Portage Lake typically sits around 72°F at the surface in August, from 43 EPA Water Quality Portal field readings (2016–2017). That is a typical value for the month, not a live reading.
How deep is Portage Lake?
- Portage Lake has a maximum depth of 18 feet and an average depth of 8 feet. The lake covers 372.44 acres.
What fish are in Portage Lake?
- Fish species found in Portage Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, yellow bullhead, yellow perch. Portage Lake is located in Aitkin County, Minnesota.
Does Portage Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Portage Lake (clouds, ice, or an off-season gap). The most recent reading was high (293,765 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Portage Lake?
- Portage Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Portage Lake. Public access is listed as yes.
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Where this data comes from
35 measurements from 1 monitoring station, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA35 samples · 2020–2022
Analytical methods
- Field measurement/observation, generic method
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
Named boat-access points from the USGS National Boat Ramps inventory