Portage Bay Lake
Cass County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for Portage Bay Lake. Here is what has been measured.
- Mesotrophic
- Impaired · Mercury
- 2 aquatic invasives
- Public access
Portage Bay Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 11.3 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
Portage Bay Lake is a mesotrophic lake in Cass County, Minnesota. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 103 other monitored lakes in Cass County, Portage Bay Lake ranks #70 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-09-07. Methodology: how these readings are compared.
What Portage Bay Lake is good for
From access and monitoring records, not editorial picks.
- Clear water11.3 ft of visibility
- Ice seasonIce-out around Apr 28
Swimming conditions
Readings onlyLow 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. Portage Bay Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
Whether Portage Bay 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 Bay Lake
These are the measurements Minnesota PCA publishes for Portage Bay 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 11.3 ft. Phosphorus 15 µg/L. Chlorophyll-a 4.9 µg/L. TSI 44.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 11.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 15µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 4.9µg/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. | 44 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Portage Bay Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Portage Bay Lake typically sits around 69°F at the surface in September. Summer average is about 71°F. Usually warmest in Jul (about 73°F) and coldest in Jun (about 68°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (68°F) to its warmest (73°F).
Typical surface water temperature by month, from 106 field readings (2022–2023) via the EPA Water Quality Portal. See the full Portage Bay Lake water temperature breakdown →
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Portage Bay Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Public Water Access Sites — Leech (Main Basin)Public Water Access Sites · MN DNR LakeFinder
Stays via Stay22
Stays near Portage Bay Lake
Compare lakeside cabins, hotels, and vacation rentals near Portage Bay 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 Bay Lake
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Follow Portage Bay Lake’s readings
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Fishing Portage Bay 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 (2022–2023). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening2 years
Phosphorus
Improving-3 µg/L/yr2 years
Chlorophyll-a
Improving-0.2 µg/L/yr2 years
Ice season
Typical ice-out
Apr 28
Earliest Apr 9, 1945 · Latest May 23, 1950
Typical ice-in
Nov 14
Earliest Nov 13, 2018 · Latest Nov 25, 2021
Most recent ice-out
May 8
2022
74 observations · Minnesota PCA ice records
EPA Impairment Status
Portage Bay Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Fish consumption.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN11-0203-01 · Official waterbody report
Nearby Lakes in Cass County
Frequently asked questions about Portage Bay Lake
Where is Portage Bay Lake?
- Portage Bay 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 Bay Lake?
- Portage Bay Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 11.3 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
Is Portage Bay Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Portage Bay Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
What is the water temperature of Portage Bay Lake?
- Portage Bay Lake typically sits around 69°F at the surface in September, from 106 EPA Water Quality Portal field readings (2022–2023). That is a typical value for the month, not a live reading.
When does Portage Bay Lake thaw?
- Portage Bay Lake typically has ice-out around Apr 28. Ice typically forms around Nov 14. The open water season is approximately 200 days.
Can I fish at Portage Bay Lake?
- Public access to Portage Bay 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.
Explore Portage Bay Lake across LakeQuality
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Where this data comes from
26 measurements from 1 monitoring station, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Leech Lake Band of Ojibwe
LEECHLAK_WQX26 samples · 2022–2023
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
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
Impairment status from EPA ATTAINS 303(d) database
Ice data from Minnesota DNR Climate