Portage Bay Lake
Portage Bay Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.3 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
- Clarity
- 11.3 ft
- Typical in August
- 72°F
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 28
- Open water
- 200 days
Next lake in Cass County
Portage Bay Lake is a mesotrophic lake in Cass County, Minnesota. Water quality is graded A based on 2 sampling years through 2023. 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. Grade methodology: LakeGrade methodology.
Watch Portage Bay Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyLow algae
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)
Good clarity, visible to about 11.3 ft. Phosphorus level: 15 µg/L. Chlorophyll-a: 4.9 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.3 ft | Not graded |
| Phosphorus | 15 µg/L | Good |
| Chlorophyll-a (Algae) | 4.9 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay 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
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Portage Bay 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 Jun (about 68°F). These are typical values by month — not a live reading.
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 →
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
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.
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
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.3 m/yr | 2 |
| Phosphorus | ↑ Improving | -3 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -0.2 µg/L/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (74 observations).
Estimated open water season: 200 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 1945-04-09 (1945) | 1950-05-23 (1950) |
| Ice-In | 2018-11-13 (2018) | 2021-11-25 (2021) |
Most recent ice-out: 2022-05-08
County Ranking
Ranked #70 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Portage Bay Lake
What is the water quality grade for Portage Bay Lake?
- Portage Bay Lake in Cass County, Minnesota has a water quality grade of A (Excellent). 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?
- Excellent for swimming, crystal clear water with minimal algae. Portage Bay Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 4.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Portage Bay Lake?
- Portage Bay Lake typically sits around 72°F at the surface in August, from 106 EPA Water Quality Portal field readings (2022–2023). That is a typical value for the month, not a live reading.
How deep is Portage Bay Lake?
- The available depth estimate for Portage Bay Lake is shallower than its measured water clarity, which cannot be right, so no depth is shown.
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.
Explore Portage Bay Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Cass County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Brainerd Lakes area
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Mississippi Headwaters, ranked by water quality
Lakes in the Pine River Watersheds (Brainerd Lakes), ranked by water quality
Moderate nutrients, good water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
Other Grade A Lakes in Minnesota
Mesotrophic Lakes in Minnesota
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)
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 size & watershed from HydroLAKES (HydroSHEDS)
Ice data from Minnesota DNR Climate