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LakeQuality
B

Big Portage (W Bay Lake

Cass County, MinnesotaMesotrophic

Big Portage (W Bay Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

Mesotrophic conditions dominate at Big Portage (W Bay Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. Big Portage (W Bay Lake reaches 23 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. The lake's 902 acres and 7.2 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Big Portage (W Bay Lake ranks 118 of 133 in Cass County — at the lower end of the locally monitored distribution.

Big Portage (W Bay Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. Walleye are documented at Big Portage (W Bay Lake, one of 13 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-08-11. Grade methodology: LakeGrade methodology.

Swimming Safety

Good for swimming, clear water with low algae levels

Water Quality Grade: B, Good

Moderate clarity, visible to about 7.5 ft. Phosphorus level: 20 µg/L. Trophic State Index: 48.

MetricValueGrade
Water Clarity (Secchi Depth)7.5 ftC
Phosphorus20 µg/LB
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)48Mesotrophic

Moderate nutrients, good water quality

Lake Details

CharacteristicValue
Maximum Depth23 ft
Surface Area902.34 acres
Shoreline Length7.2 mi
Littoral Zone100%
Public AccessYes

Fish Species

Click a species to see all Minnesota and Wisconsin lakes where it is found.

→ Best fishing times for Big Portage (W Bay Lake (14-day solunar calendar)

→ Is it safe to eat fish from Big Portage (W Bay Lake? (mercury & PFAS guide)

Big Portage (W Bay Lake fishing regulations (limits, seasons, special rules)

Water Quality Trend: Improving

Based on 5 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Improving+0.145 m/yr5
Phosphorus Improving-2.05 µg/L/yr5
See year-by-year chart →

Location

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County Ranking

Ranked #118 of 133 lakes in Cass County

Cleaner Lakes Within 30 Miles

Big Portage (W Bay Lake holds Grade B. 3 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Cass County

DNR Fisheries Survey Summary

8 surveys on file from MN DNR Fisheries. Most recent: 2023-07-10 (Standard Survey).

Top Species by Catch Rate

SpeciesAvg CPUEAvg Weight
Bluntnose Minnow28.67
BCS25.00
BNS15.00
Bluegill13.930.22 lb
Yellow Perch10.520.17 lb
Northern Pike4.841.54 lb

CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.

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

450 fish · 38 in · 2023-07-10
2331170345678

Yellow Perch

52 fish · 58 in · 2023-07-10
361805678

Northern Pike

57 fish · 933 in · 2023-07-10
1050101214161820222426283032

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…

Source: MN DNR LakeFinder Fisheries Lake Survey

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.

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Lake details from Minnesota DNR LakeFinder

Most recent sample: 2024-08-11

Monitoring stations: 2