Big Portage (W Bay Lake
Cass County, Minnesota902 acresView mapDirections
This is the name Minnesota PCA records for this water. It can describe one sampling location rather than the water as a whole.
Minnesota PCA publishes the water-quality measurements for Big Portage (W Bay Lake. Here is what has been measured.
- Mesotrophic
- Impaired · Mercury
- 23 ft max depth
- Public access
Big Portage (W Bay Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 8.5 ft visibility. Phosphorus: 18.5 µg/L. Chlorophyll-a (algae): 5.6 µg/L. Maximum depth: 23 ft. Surface area: 902.34 acres.
Minnesota DNR's Standard Survey on July 10, 2023 caught 0.88 walleye per gill net at Big Portage (W Bay Lake. DNR survey details →
Free interactive depth-contour map of Big Portage (W Bay Lake, reaching a maximum surveyed depth of 15 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Big Portage (W Bay Lake is a 902-acre mesotrophic lake in Cass County, Minnesota with a maximum depth of 23 feet. Overall water quality is improving over recent sampling years. The lake supports 13 documented fish species including black crappie, bluegill, and bowfin (dogfish). Public access is available. Compared to the 103 other monitored lakes in Cass County, Big Portage (W Bay Lake ranks #60 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-02. Methodology: how these readings are compared.
What Big Portage (W Bay Lake is good for
From access and monitoring records, not editorial picks.
- Fishing13 species recorded
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. Big Portage (W Bay Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury. Check local advisories before you swim.
Whether Big Portage (W 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 Big Portage (W Bay Lake
These are the measurements Minnesota PCA publishes for Big Portage (W Bay 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 8.5 ft. Phosphorus 18.5 µg/L. Chlorophyll-a 5.6 µg/L. TSI 47.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 8.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 18.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 5.6µg/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. | 47 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Big Portage (W Bay Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Big Portage (W Bay Lake typically sits around 53°F at the surface in October. Summer average is about 74°F. Usually warmest in Jun (about 74°F) and coldest in Oct (about 53°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (53°F) to its warmest (74°F).
Typical surface water temperature by month, from 42 field readings (2016–2025) via the EPA Water Quality Portal. See the full Big Portage (W Bay Lake water temperature breakdown →
Minnesota DNR's Standard Survey on July 10, 2023 caught 0.88 walleye per gill net at Big Portage (W Bay Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Big Portage (W Bay Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
8 surveys on file from MN DNR Fisheries. Most recent: 2023-07-10 (Standard Survey).
8 surveys on file · most recent 2023-07-10 (Standard Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluntnose Minnow | 28.67 | ||
| Bluegill | 13.93 | 3–8 in 2023-07-10 | 0.22 lb |
| Yellow Perch | 10.52 | 5–8 in 2023-07-10 | 0.17 lb |
| Northern Pike | 4.84 | 9–33 in 2023-07-10 | 1.54 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.
Bluegill
Yellow Perch
Northern Pike
From the 2023-07-10 survey
Big Portage (Rice Portage) Lake is a 902-acre lake with 7.22 miles of shoreline and a maximum depth of 23 feet located northeast of Backus, MN. The Minnesota Department of Natural Resources (MNDNR) has classified Minnesota's lakes into 43 different classes based on physical, chemical and other characteristics. Big…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Big Portage (W Bay Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Big PortageFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Big Portage (1476)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — Big PortageFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — Big PortagePublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
23 ft
Surface area
902 acres
Shoreline
7.2 mi
Littoral zone
100%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
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Fish Species
Click a species to see every lake where it is documented.
Fishing Big Portage (W Bay Lake
- → Big Portage (W Bay Lake fishing: DNR survey catch rates, species & stocking
- → Big Portage (W Bay Lake fishing forecast & best times (species outlook + 14-day solunar calendar)
- → Big Portage (W Bay Lake fishing regulations (limits, seasons, special rules)
- → Is it safe to eat fish from Big Portage (W Bay Lake? (mercury & PFAS guide)
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Improving6 years
Phosphorus
Improving-1.59 µg/L/yr6 years
Chlorophyll-a
Improving-0.64 µg/L/yr6 years
EPA Impairment Status
Big Portage (W 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 MN11-0308-01 · Official waterbody report
Nearby Lakes in Cass County
Frequently asked questions about Big Portage (W Bay Lake
Where is Big Portage (W Bay Lake?
- Big Portage (W Bay Lake is in Cass County, Minnesota. This is the name Minnesota PCA records for this water. It can describe one sampling location rather than the water as a whole. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Big Portage (W Bay Lake?
- Big Portage (W Bay Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 8.5 ft visibility. Phosphorus: 18.5 µg/L. Chlorophyll-a (algae): 5.6 µg/L. Maximum depth: 23 ft. Surface area: 902.34 acres.
Is Big Portage (W Bay Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Big Portage (W 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 Big Portage (W Bay Lake?
- Big Portage (W Bay Lake typically sits around 53°F at the surface in October, from 42 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Big Portage (W Bay Lake?
- Big Portage (W Bay Lake has a maximum depth of 23 feet. The lake covers 902.34 acres.
What fish are in Big Portage (W Bay Lake?
- Fish species found in Big Portage (W Bay Lake include black crappie, bluegill, bowfin (dogfish), brown bullhead, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, walleye, white sucker, yellow bullhead, yellow perch. Big Portage (W Bay Lake is located in Cass County, Minnesota.
What did the DNR fisheries survey find at Big Portage (W Bay Lake?
- Minnesota DNR's Standard Survey on July 10, 2023 caught 0.88 walleye per gill net at Big Portage (W Bay Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Big Portage (W Bay Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Can I fish at Big Portage (W Bay Lake?
- Public access to Big Portage (W 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 Big Portage (W Bay Lake across LakeQuality
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Where this data comes from
75 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA75 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (2)
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
Lake details from Minnesota DNR LakeFinder