Portage Lake
Cass County, Minnesota1,539 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Portage Lake. Here is what has been measured.
- Mesotrophic
- zebra mussel
- 55 ft max depth
- Public access
Portage Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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.
Minnesota DNR's Targeted Survey on August 16, 2021 caught 17.31 largemouth bass per hour of electrofishing at Portage Lake. DNR survey details →
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. 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. 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. Methodology: how these readings are compared.
What Portage Lake is good for
From access and monitoring records, not editorial picks.
- Fishing15 species recorded
- Ice seasonIce-out around May 5
- Deep water55 ft surveyed max depth
- Big water1,539 acres
Swimming conditions
Readings onlyModerate algae
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 Portage Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Portage Lake
These are the measurements Minnesota PCA publishes for Portage Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 7.5 ft. Phosphorus 22 µg/L. Chlorophyll-a 7.1 µg/L. TSI 49.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 7.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 22µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 7.1µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 49 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Portage Lake
Answers come straight from the public measurements and survey records on this page.
Minnesota DNR's Targeted Survey on August 16, 2021 caught 17.31 largemouth bass per hour of electrofishing at Portage Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Portage Lake’s water-quality measurements separately, and the water-quality trend over 2 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
6 surveys on file from MN DNR Fisheries. Most recent: 2021-08-16 (Targeted Survey).
6 surveys on file · most recent 2021-08-16 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Yellow Perch | 43.78 | 3–9 in 2021-07-19 | 0.13 lb |
| Black Bullhead | 26.81 | 0.34 lb | |
| Bluegill | 7.12 | 2–9 in 2021-07-19 | 0.15 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and 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.
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
Lake Details
Max depth
55 ft
Surface area
1,539 acres
Shoreline
7.9 mi
Littoral zone
44%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
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Stays near Portage Lake
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Top-rated places to stay near Portage Lake
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Follow Portage Lake’s readings
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Fish Species
Click a species to see every 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.
Water quality readings over time
2 seasons of samples on record (2024–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Improving2 years
Ice season
Typical ice-out
May 5
Earliest Apr 13, 2015 · Latest May 10, 2008
Typical ice-in
Nov 25
Earliest Nov 20, 2007 · Latest Nov 27, 2021
Most recent ice-out
May 5
2022
6 observations · Minnesota PCA ice records
Nearby Lakes in Cass County
Frequently asked questions about Portage Lake
Where is Portage Lake?
- Portage Lake is a lake in Cass County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Portage Lake?
- Portage Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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.
What did the DNR fisheries survey find at Portage Lake?
- Minnesota DNR's Targeted Survey on August 16, 2021 caught 17.31 largemouth bass per hour of electrofishing at Portage Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Portage Lake’s water-quality measurements separately, and the water-quality trend over 2 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
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.
Can I fish at Portage Lake?
- Public access to Portage Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
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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)
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 details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate