Portage Lake
Portage Lake in Cass County, Minnesota has a water quality grade of C (Fair). Water clarity: 7.5 ft visibility. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 7.1 µg/L. Maximum depth: 55 ft. Surface area: 1538.61 acres.
- Clarity
- 7.5 ft
- Max depth
- 55 ft
- Area
- 1,539 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- May 5
- Open water
- 204 days
Next lake in Cass County
Free interactive depth-contour map of Portage Lake, reaching a maximum surveyed depth of 50 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Portage Lake is a 1,539-acre mesotrophic lake in Cass County, Minnesota with a maximum depth of 55 feet. Water quality is graded C based on 3 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 15 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 2 public boat landings. Compared to the 103 other monitored lakes in Cass County, Portage Lake ranks #88 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Moderate clarity, visible to about 7.5 ft. Phosphorus level: 22 µg/L. Chlorophyll-a: 7.1 µg/L. Trophic State Index: 49.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.5 ft | Not graded |
| Phosphorus | 22 µg/L | Good |
| Chlorophyll-a (Algae) | 7.1 µg/L | Good |
| Trophic State Index (TSI) | 49 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Portage Lake
Compare lakeside cabins, hotels, and vacation rentals near Portage Lake in Cass 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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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 55 ft |
| Surface Area | 1,539 acres |
| Shoreline Length | 7.9 mi |
| Littoral Zone | 44% |
| Public Access | Yes |
Recreation & Access
- Portage LakePublic
- Iowana Beach ResortSemi-private
Fish Species
Click a species to see every graded lake where it is documented.
Fishing 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.
DNR Fisheries Survey Summary
6 surveys on file from MN DNR Fisheries. Most recent: 2021-08-16 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 43.78 | 0.13 lb |
| BKF | 32.71 | — |
| Black Bullhead | 26.81 | 0.34 lb |
| Bluegill | 7.12 | 0.15 lb |
| CNM | 5.16 | — |
| IOD | 4.82 | — |
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.
Yellow Perch
Bluegill
From the 2021-08-16 survey
A targeted survey of nearshore fish species in Portage Lake was conducted on August 16-17, 2021, by Index of Biological Integrity (IBI) Program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Portage Lake. 4 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 (1504)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — PortageFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — PortagePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.92 m/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (6 observations).
Estimated open water season: 204 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2015-04-13 (2015) | 2008-05-10 (2008) |
| Ice-In | 2007-11-20 (2007) | 2021-11-27 (2021) |
Most recent ice-out: 2022-05-05
County Ranking
Ranked #88 of 104 lakes in Cass County
Nearby Lakes With Higher Grades
Portage Lake holds Grade C. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Cass County
Frequently asked questions about Portage Lake
What is the water quality grade for Portage Lake?
- Portage Lake in Cass County, Minnesota has a water quality grade of C (Fair). Water clarity: 7.5 ft visibility. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 7.1 µg/L. Maximum depth: 55 ft. Surface area: 1538.61 acres.
Is Portage Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Portage Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 7.1 µg/L. Always check local health department advisories before swimming.
How deep is Portage Lake?
- Portage Lake has a maximum depth of 55 feet. The lake covers 1538.61 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, rock bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Portage Lake is located in Cass County, Minnesota.
When does Portage Lake thaw?
- Portage Lake typically has ice-out around May 5. Ice typically forms around Nov 25. The open water season is approximately 204 days.
Are there boat ramps on Portage Lake?
- Portage Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Portage Lake, Iowana Beach Resort. Public access is listed as yes.
Explore Portage Lake across LakeGrade
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Where this data comes from
199 measurements from 4 monitoring stations, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA103 samples · 2021–2025 - Leech Lake Band of Ojibwe
LEECHLAK_WQX96 samples · 2023–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Nitrate-Nitrite Nitrogen by Colorimetry
Monitoring station identifiers (4)
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
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate