Big Deep Lake
Big Deep Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 19.4 ft visibility. Phosphorus: 7 µg/L. Chlorophyll-a (algae): 1.9 µg/L. Maximum depth: 107 ft. Surface area: 535.75 acres.
- Clarity
- 19.4 ft
- Max depth
- 107 ft
- Area
- 536 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
- Public access
- No
Next lake in Cass County
Big Deep Lake is a 536-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 107 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 bullhead, black crappie, and bluegill. No public access — the lake is private or restricted. Compared to the 103 other monitored lakes in Cass County, Big Deep Lake ranks #85 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-15. Grade methodology: LakeGrade 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)
Crystal clear, you can see 19.4 ft down. Phosphorus level: 7 µg/L. Chlorophyll-a: 1.9 µg/L. Trophic State Index: 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 19.4 ft | Not graded |
| Phosphorus | 7 µg/L | Good |
| Chlorophyll-a (Algae) | 1.9 µg/L | Good |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Big Deep Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Deep 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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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 107 ft |
| Surface Area | 536 acres |
| Shoreline Length | 5 mi |
| Littoral Zone | 9% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Big Deep Lake
DNR Fisheries Survey Summary
3 surveys on file from MN DNR Fisheries. Most recent: 1995-08-14 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Northern Pike | 7.57 | 1.11 lb |
| Bluegill | 6.04 | 0.18 lb |
| Yellow Bass | 5.00 | 0.57 lb |
| Rock Bass | 3.47 | 0.31 lb |
| Black Bullhead | 2.94 | 0.48 lb |
| Walleye | 1.72 | 2.46 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.
Northern Pike
Bluegill
Yellow Bass
Rock Bass
From the 1995-08-14 survey
Big Deep Lake is a 484 acre lake with a maximum depth of 107 feet. It is located six miles east of Hackensack in northern Cass County. The Minnesota Department of Natural Resources (DNR) has classified Minnesota's lakes into 43 different types, based on physical, chemical, and other characteristics. Big Deep Lake is…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Big Deep Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Big DeepFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Big Deep (1663)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — Big DeepFish Stocking History · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.579 m/yr | 4 |
| Phosphorus | ↑ Improving | -1.93 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -0.29 µg/L/yr | 4 |
EPA Impairment Status
Big Deep 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 MN11-0270-00 · Official waterbody report · Matched by proximity (2.22 km)
County Ranking
Ranked #85 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Big Deep Lake
What is the water quality grade for Big Deep Lake?
- Big Deep Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 19.4 ft visibility. Phosphorus: 7 µg/L. Chlorophyll-a (algae): 1.9 µg/L. Maximum depth: 107 ft. Surface area: 535.75 acres.
Is Big Deep Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Big Deep Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.9 µg/L. Always check local health department advisories before swimming.
How deep is Big Deep Lake?
- Big Deep Lake has a maximum depth of 107 feet. The lake covers 535.75 acres.
What fish are in Big Deep Lake?
- Fish species found in Big Deep Lake include black bullhead, black crappie, bluegill, brown bullhead, largemouth bass, northern pike, pumpkinseed, rock bass, smallmouth bass, walleye, white sucker, yellow bullhead, yellow perch. Big Deep Lake is located in Cass County, Minnesota.
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Where this data comes from
41 measurements from 1 monitoring station, 2023–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA41 samples · 2023–2025
Analytical methods
- Field measurement/observation, generic method
- 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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder