Outlet of Onamia Lake on the Rum River
Outlet of Onamia Lake on the Rum River in Mille Lacs County, Minnesota has a water quality grade of A (Excellent). Phosphorus: 21.8 µg/L. Chlorophyll-a (algae): 0.6 µg/L. Maximum depth: 10 ft. Surface area: 1043.71 acres.
- Max depth
- 10 ft
- Area
- 1,044 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 4
Next lake in Mille Lacs County
Outlet of Onamia Lake on the Rum River is a 1,044-acre cold, clear oligotrophic lake in Mille Lacs County, Minnesota with a maximum depth of 10 feet. Water quality is graded A based on 3 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 8 other monitored lakes in Mille Lacs County, Outlet of Onamia Lake on the Rum River ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-08. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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)
No clarity data. Phosphorus level: 21.8 µg/L. Chlorophyll-a: 0.6 µg/L. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 21.8 µg/L | Good |
| Chlorophyll-a (Algae) | 0.6 µg/L | Good |
| Trophic State Index (TSI) | 37 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Outlet of Onamia Lake on the Rum River
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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 10 ft |
| Surface Area | 1,044 acres |
| Shoreline Length | 17.8 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Onamia LakePublic
Fishing Outlet of Onamia Lake on the Rum River
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
2 surveys on file from MN DNR Fisheries. Most recent: 1989-06-13 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 5.41 | 0.26 lb |
| Black Bullhead | 5.22 | 0.38 lb |
| Yellow Bass | 3.88 | 0.53 lb |
| Northern Pike | 3.58 | 0.9 lb |
| Pumpkinseed | 2.87 | 0.1 lb |
| White Sucker | 2.68 | 1.81 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1989-06-13 survey
FISH POPULATION IS MOSTLY ROUGHFISH: SUCKERS, CARP BOWFIN AND BULLHEADS WHICH ARE ALL ABOVE THEIR STATE MEDIANS. NORTHERN PIKE ARE JUST ABOVE THE AVERAGE BUT ARE SMALL IN SIZE. THE WALLEYE POPULA- TION IS LOW AND YELLOW PERCH ARE AT HALF OF THE STATE AVERAGE IN NUMBER. SOME BLUEGILLS WERE CAUGHT IN THE NATURAL…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Outlet of Onamia Lake on the Rum River. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — OnamiaFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Onamia (0341)Aquatic Plant Report · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↑ Improving | -4.1 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -0.3 µg/L/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (4 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2015-03-30 (2015) | 2019-04-20 (2019) |
Most recent ice-out: 2020-04-05
County Ranking
Ranked #3 of 9 lakes in Mille Lacs County
Nearby Lakes in Mille Lacs County
Frequently asked questions about Outlet of Onamia Lake on the Rum River
What is the water quality grade for Outlet of Onamia Lake on the Rum River?
- Outlet of Onamia Lake on the Rum River in Mille Lacs County, Minnesota has a water quality grade of A (Excellent). Phosphorus: 21.8 µg/L. Chlorophyll-a (algae): 0.6 µg/L. Maximum depth: 10 ft. Surface area: 1043.71 acres.
Is Outlet of Onamia Lake on the Rum River safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Outlet of Onamia Lake on the Rum River has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 0.6 µg/L. Always check local health department advisories before swimming.
How deep is Outlet of Onamia Lake on the Rum River?
- Outlet of Onamia Lake on the Rum River has a maximum depth of 10 feet. The lake covers 1043.71 acres.
When does Outlet of Onamia Lake on the Rum River thaw?
- Outlet of Onamia Lake on the Rum River typically has ice-out around Apr 4.
Are there boat ramps on Outlet of Onamia Lake on the Rum River?
- Outlet of Onamia Lake on the Rum River has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Onamia Lake. Public access is listed as yes.
Explore Outlet of Onamia Lake on the Rum River across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Species activity outlook by water temperature and season
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Low nutrients, clear water, excellent for swimming
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Where this data comes from
20 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Mille Lacs Band of Ojibwe DNR/Environment
MLBO_DNR_WQX20 samples · 2023–2024
Analytical methods
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 10200 H ~ Chlorophyll a-b-c Determination
- SM 4500-PJ and NO3-F
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
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