Bertha Lake
Crow Wing County, Minnesota337 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Bertha Lake. Here is what has been measured.
- Oligotrophic
- zebra mussel
- 64 ft max depth
Bertha Lake in Crow Wing County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 17.1 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 2.4 µg/L. Maximum depth: 64 ft. Surface area: 336.87 acres.
Minnesota DNR's Standard Survey on June 10, 2024 caught 1.44 walleye per gill net at Bertha Lake. DNR survey details →
Bertha Lake is a 337-acre cold, clear oligotrophic lake in Crow Wing County, Minnesota with a maximum depth of 64 feet. Overall water quality is declining over recent sampling years. The lake supports 22 documented fish species including black bullhead, black crappie, and bluegill. No public access — the lake is private or restricted. Compared to the 84 other monitored lakes in Crow Wing County, Bertha Lake ranks #53 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-14. Methodology: how these readings are compared.
Bertha Lake covers about 340 acres in Crow Wing County. The median ice-out date is April 18, which is when the open-water season begins. For a place on the water, look through cabin and lake-house rentals near Bertha Lake on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.
What Bertha Lake is good for
From access and monitoring records, not editorial picks.
- Clear water17.1 ft of visibility
- Fishing22 species recorded
- Ice seasonIce-out around Apr 18
- Deep water64 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 Bertha 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 Bertha Lake
These are the measurements Minnesota PCA publishes for Bertha 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 17.1 ft down. Phosphorus 13 µg/L. Chlorophyll-a 2.4 µg/L. TSI 39.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 17.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 13µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.4µg/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. | 39 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Bertha Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Bertha Lake typically sits around 61°F at the surface in September. Summer average is about 63°F. Usually warmest in Aug (about 64°F) and coldest in May (about 55°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (55°F) to its warmest (64°F).
Typical surface water temperature by month, from 189 field readings (2017–2025) via the EPA Water Quality Portal. See the full Bertha Lake water temperature breakdown →
Minnesota DNR's Standard Survey on June 10, 2024 caught 1.44 walleye per gill net at Bertha Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Bertha Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
11 surveys on file from MN DNR Fisheries. Most recent: 2024-08-14 (Targeted Survey).
11 surveys on file · most recent 2024-08-14 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 31.89 | 2–8 in 2024-06-10 | 0.13 lb |
| Bluntnose Minnow | 18.42 | ||
| Tullibee (Cisco) | 15.55 | 8–18 in 2024-06-10 | 0.37 lb |
| Yellow Perch | 8.35 | 4–11 in 2024-06-10 | 0.15 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
Tullibee (Cisco)
Yellow Perch
From the 2024-08-14 survey
Temperature and dissolved oxygen profiles were collected in the deepest basin in Bertha Lake on August 14, 2024, to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Lake Whitefish, the most sensitive coldwater species present in this lake (Cisco are also present).…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Bertha Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — BerthaFisheries Lake Survey · MN DNR LakeFinder
Lake Details
Max depth
64 ft
Surface area
337 acres
Shoreline
3.9 mi
Littoral zone
42%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Stays via Stay22
Stays near Bertha Lake
Compare lakeside cabins, hotels, and vacation rentals near Bertha Lake in Crow Wing 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 Bertha Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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Fish Species
Click a species to see every lake where it is documented.
Fishing Bertha Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Stable6 years
Phosphorus
Worsening+1.54 µg/L/yr6 years
Chlorophyll-a
Stable-0.02 µg/L/yr6 years
Ice season
Typical ice-out
Apr 18
Earliest Mar 17, 2024 · Latest May 6, 2022
Most recent ice-out
Apr 15
2025
11 observations · Minnesota PCA ice records
Nearby Lakes in Crow Wing County
Frequently asked questions about Bertha Lake
Where is Bertha Lake?
- Bertha Lake is a lake in Crow Wing County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Bertha Lake?
- Bertha Lake in Crow Wing County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 17.1 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 2.4 µg/L. Maximum depth: 64 ft. Surface area: 336.87 acres.
Is Bertha Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Bertha Lake?
- Bertha Lake typically sits around 61°F at the surface in September, from 189 EPA Water Quality Portal field readings (2017–2025). That is a typical value for the month, not a live reading.
How deep is Bertha Lake?
- Bertha Lake has a maximum depth of 64 feet. The lake covers 336.87 acres.
What fish are in Bertha Lake?
- Fish species found in Bertha Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, burbot, greater redhorse, green sunfish, hybrid sunfish, lake whitefish, largemouth bass, northern pike, northern sunfish, pumpkinseed, rock bass, shorthead redhorse, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Bertha Lake is located in Crow Wing County, Minnesota.
What did the DNR fisheries survey find at Bertha Lake?
- Minnesota DNR's Standard Survey on June 10, 2024 caught 1.44 walleye per gill net at Bertha Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Bertha Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
When does Bertha Lake thaw?
- Bertha Lake typically has ice-out around Apr 18.
Can I fish at Bertha Lake?
- Public access to Bertha 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 Bertha Lake across LakeQuality
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Where this data comes from
106 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA106 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
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 details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate