Big Portage (W Bay Lake
Big Portage (W Bay Lake in Cass County, Minnesota has a water quality grade of A (Excellent). 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 surveys at Big Portage (W Bay Lake average 4.84 northern pike per unit of sampling effort (CPUE) across 8 surveys. The most recent is a Standard Survey dated July 10, 2023. Length samples in the latest survey that recorded them ran 9–33 inches. DNR survey details →
- Clarity
- 8.5 ft
- Typical in August
- 74°F
- Max depth
- 23 ft
- Area
- 902 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
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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. Water quality is graded A based on 2 sampling years through 2025. 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 with 1 public boat landing. 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. Grade methodology: LakeQuality methodology.
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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)
Moderate clarity, visible to about 8.5 ft. Phosphorus level: 18.5 µg/L. Chlorophyll-a: 5.6 µg/L. Trophic State Index: 47.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.5 ft | Not graded |
| Phosphorus | 18.5 µg/L | Good |
| Chlorophyll-a (Algae) | 5.6 µg/L | Good |
| Trophic State Index (TSI) | 47 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Big Portage (W Bay Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Portage (W 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.
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Water Temperature
Big Portage (W Bay Lake typically sits around 74°F at the surface in August. 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.
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 surveys at Big Portage (W Bay Lake average 4.84 northern pike per unit of sampling effort (CPUE) across 8 surveys. The most recent is a Standard Survey dated July 10, 2023. Length samples in the latest survey that recorded them ran 9–33 inches.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Big Portage (W Bay Lake A from EPA Water Quality Portal chemistry, 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).
Top Species by Catch Rate
| Species | Avg catch rate (CPUE) | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 28.67 | — |
| Bluegill | 13.93 | 0.22 lb |
| Yellow Perch | 10.52 | 0.17 lb |
| Northern Pike | 4.84 | 1.54 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE means more abundant in standardized sampling. This 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
| Characteristic | Value |
|---|---|
| Maximum Depth | 23 ft |
| Surface Area | 902 acres |
| Shoreline Length | 7.2 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Recreation & Access
- Big Portage LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Big Portage (W Bay Lake
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.129 m/yr | 6 |
| Phosphorus | ↑ Improving | -1.59 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.64 µg/L/yr | 6 |
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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN11-0308-01 · Official waterbody report · Matched by proximity (0.43 km)
County Ranking
Ranked #60 of 104 lakes in Cass County
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 a lake in Cass County, Minnesota. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Big Portage (W Bay Lake?
- Big Portage (W Bay Lake in Cass County, Minnesota has a water quality grade of A (Excellent). 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?
- Excellent for swimming, crystal clear water with minimal algae. Big Portage (W Bay Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 5.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Big Portage (W Bay Lake?
- Big Portage (W Bay Lake typically sits around 74°F at the surface in August, 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 surveys at Big Portage (W Bay Lake average 4.84 northern pike per unit of sampling effort (CPUE) across 8 surveys. The most recent is a Standard Survey dated July 10, 2023. Length samples in the latest survey that recorded them ran 9–33 inches. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Big Portage (W Bay Lake A from EPA Water Quality Portal chemistry, 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.
Are there boat ramps on Big Portage (W Bay Lake?
- Big Portage (W Bay Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Big Portage Lake. Public access is listed as yes.
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)
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory