Carlos Lake
Carlos Lake in Douglas County, Minnesota has a water quality grade of A (Excellent). Water clarity: 18 ft visibility. Phosphorus: 13.5 µg/L. Chlorophyll-a (algae): 2.1 µg/L. Maximum depth: 163 ft. Surface area: 2605.11 acres.
- Clarity
- 18 ft
- Typical in August
- 73°F
- Max depth
- 163 ft
- Area
- 2,605 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 21
Next lake in Douglas County
Free interactive depth-contour map of Carlos Lake, reaching a maximum surveyed depth of 150 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Carlos Lake is a 2,605-acre cold, clear oligotrophic lake in Douglas County, Minnesota with a maximum depth of 163 feet (50-foot average). Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 21 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 4 public boat landings. Compared to the 36 other monitored lakes in Douglas County, Carlos Lake ranks #18 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-01. 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 18 ft down. Phosphorus level: 13.5 µg/L. Chlorophyll-a: 2.1 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 18 ft | Not graded |
| Phosphorus | 13.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.1 µg/L | Good |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Carlos Lake
Compare lakeside cabins, hotels, and vacation rentals near Carlos Lake in Douglas 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
Carlos Lake typically sits around 73°F at the surface in August. Summer average is about 72°F. Usually warmest in Jul (about 76°F) and coldest in May (about 47°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 63 field readings (2011–2025) via the EPA Water Quality Portal. See the full Carlos Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 163 ft |
| Average Depth | 50 ft |
| Surface Area | 2,605 acres |
| Shoreline Length | 12.8 mi |
| Littoral Zone | 35% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Lake Carlos (East)Public
- Lake Carlos State ParkPublic
- Lake Carlos (West)Public
- Lake Carlos (Northeast)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Carlos 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.
DNR Fisheries Survey Summary
14 surveys on file from MN DNR Fisheries. Most recent: 2024-08-20 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 35.04 | — |
| CSH | 34.03 | — |
| Largemouth Bass | 18.69 | 0.69 lb |
| Bluegill | 18.02 | 0.14 lb |
| JND | 13.12 | — |
| BKS | 9.45 | — |
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.
Largemouth Bass
Bluegill
From the 2024-08-20 survey
A targeted survey of nearshore fish species in Lake Carlos was conducted beginning on August 20, 2024, by Index of Biological Integrity (IBI) Program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible.…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Carlos Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — CarlosFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Carlos (1074)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — CarlosFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — CarlosPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.393 m/yr | 6 |
| Phosphorus | ↓ Declining | +0.6 µg/L/yr | 6 |
| Chlorophyll-a | → Stable | 0 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (17 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-12 (2024) | 2013-05-13 (2013) |
| Ice-In | 2016-12-17 (2016) | 2016-12-17 (2016) |
Most recent ice-out: 2024-03-12
Reservoir Info (USACE NID)
Carlos Lake is a man-made reservoir impounded by the Lake Carlos (completed 1993), built primarily for recreation on the Long Prairie River; other-type dam, 7 ft tall.
- Surface area
- 183 ac
- Normal storage
- 156,000 ac-ft
- Max storage
- 156,000 ac-ft
- Drainage area
- 247 sq mi
- Hazard class
- Undetermined
- Owner
- MNDNR
Source: USACE National Inventory of Dams, NID ID MN01118 · Operator website
EPA Impairment Status
Carlos Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN21-0057-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Carlos Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Carlos WwtpCarlos · 3.3 mi away · NPDES MN0023019Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #18 of 37 lakes in Douglas County
Nearby Lakes in Douglas County
Frequently asked questions about Carlos Lake
What is the water quality grade for Carlos Lake?
- Carlos Lake in Douglas County, Minnesota has a water quality grade of A (Excellent). Water clarity: 18 ft visibility. Phosphorus: 13.5 µg/L. Chlorophyll-a (algae): 2.1 µg/L. Maximum depth: 163 ft. Surface area: 2605.11 acres.
Is Carlos Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Carlos Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.1 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Carlos Lake?
- Carlos Lake typically sits around 73°F at the surface in August, from 63 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
How deep is Carlos Lake?
- Carlos Lake has a maximum depth of 163 feet and an average depth of 50 feet. The lake covers 2605.11 acres.
What fish are in Carlos Lake?
- Fish species found in Carlos Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, common carp, greater redhorse, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, shorthead redhorse, smallmouth bass, sunfish, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Carlos Lake is located in Douglas County, Minnesota.
When does Carlos Lake thaw?
- Carlos Lake typically has ice-out around Apr 21.
Are there boat ramps on Carlos Lake?
- Carlos Lake has 4 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Lake Carlos (East), Lake Carlos State Park, Lake Carlos (West), Lake Carlos (Northeast). Public access is listed as yes.
Explore Carlos Lake across LakeGrade
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Where this data comes from
175 measurements from 4 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
MNPCA175 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
- Phosphorus by Colorimetry
Monitoring station identifiers (4)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate