Big Deep Lake
Cass County, Minnesota536 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Big Deep Lake. Here is what has been measured.
- Oligotrophic
- 107 ft max depth
Big Deep Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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.
Minnesota DNR's Standard Survey on August 14, 1995 caught 1.56 walleye per gill net at Big Deep Lake. Length samples in the latest survey that recorded them ran 12–24 inches. DNR survey details →
Big Deep Lake is a 536-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 107 feet. 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. Methodology: how these readings are compared.
Big Deep Lake covers about 540 acres in Cass County. Vrbo is where to look for cabins and lake homes around Big Deep Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Big Deep Lake is good for
From access and monitoring records, not editorial picks.
- Clear water19.4 ft of visibility
- Fishing13 species recorded
- Deep water107 ft surveyed max depth
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. Check local advisories before you swim.
Whether Big Deep 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 Deep Lake
These are the measurements Minnesota PCA publishes for Big Deep Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 19.4 ft down. Phosphorus 7 µg/L. Chlorophyll-a 1.9 µg/L. TSI 35.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 19.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 7µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.9µg/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. | 35 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Big Deep Lake
Answers come straight from the public measurements and survey records on this page.
Minnesota DNR's Standard Survey on August 14, 1995 caught 1.56 walleye per gill net at Big Deep Lake. Length samples in the latest survey that recorded them ran 12–24 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Big Deep Lake’s water-quality measurements separately, and the water-quality trend over 4 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
3 surveys on file from MN DNR Fisheries. Most recent: 1995-08-14 (Standard Survey).
3 surveys on file · most recent 1995-08-14 (Standard Survey)
31 years old| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Northern Pike | 7.57 | 6–31 in 1995-08-14 | 1.11 lb |
| Bluegill | 6.04 | 3–8 in 1995-08-14 | 0.18 lb |
| Yellow Bullhead | 5.00 | 7–12 in 1995-08-14 | 0.57 lb |
| Rock Bass | 3.47 | 3–9 in 1995-08-14 | 0.31 lb |
| Black Bullhead | 2.94 | 8–11 in 1995-08-14 | 0.48 lb |
| Walleye | 1.72 | 12–24 in 1995-08-14 | 2.46 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.
Northern Pike
Bluegill
Yellow Bullhead
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
Lake Details
Max depth
107 ft
Surface area
536 acres
Shoreline
5 mi
Littoral zone
9%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
71 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,335 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays 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.
Top-rated places to stay near Big Deep Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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 →
Follow Big Deep Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fish Species
Click a species to see every lake where it is documented.
Fishing Big Deep Lake
Water Quality Trend: Improving
Based on 4 years of monitoring (2020–2025).
Water clarity
Improving4 years
Phosphorus
Improving-1.93 µg/L/yr4 years
Chlorophyll-a
Improving-0.29 µg/L/yr4 years
Nearby Lakes in Cass County
Frequently asked questions about Big Deep Lake
Where is Big Deep Lake?
- Big Deep Lake is a lake in Cass County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Big Deep Lake?
- Big Deep Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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.
What did the DNR fisheries survey find at Big Deep Lake?
- Minnesota DNR's Standard Survey on August 14, 1995 caught 1.56 walleye per gill net at Big Deep Lake. Length samples in the latest survey that recorded them ran 12–24 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Big Deep Lake’s water-quality measurements separately, and the water-quality trend over 4 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Can I fish at Big Deep Lake?
- Public access to Big Deep Lake is listed as no on the lake record, so confirm before you make the trip. 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 Deep Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and the cleanest 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 readings
Lakes in the Mississippi Headwaters, ranked by water quality
Lakes in the Pine River Watersheds (Brainerd Lakes), ranked by water quality
Minnesota's cleanest lakes, ranked on agency measurements
More lakes in Minnesota
Other Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Compare Big Deep Lake With Nearby Lakes
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)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder