O’Conners Lake
O’Connors Lake
Lake Description
O’Connors Lake is located in Denmark Township amongst primarily agricultural lands. Water flows from O’Connors Creek into O’Connors Lake, which is landlocked with no surface outlet. O’Connors Lake is typically shallow enough for aquatic plants to grow over the entire waterbody and for the lake to mix many times per year.
Lake Details
| Location | Denmark Township |
| Shallow/Deep | Shallow |
| Surface Area | 25 acres |
| Average | 5 ft |
| Maximum Depth | 16 ft |
| Direct Watershed Area | 1,698 acres |
| Impairment Status | Impaired for nutrients since 2026 |
| Downstream Waterbody | Mississippi River |
Water Quality in O’Connors Lake
O’Connors Lake sits amongst primarily agricultural land, which impacts the water quality. Agricultural runoff transports nutrients from fertilizers, increasing algal blooms and worsening water quality. O’Connors Lake was listed on the impaired waters list in 2026.
Despite its proximity, O’Connors Lake and Creek have tested within the state standard for summer average chlorophyll-a concentrations.
Chloride concentrations are monitored and are typically below the state standard.
O’Connors Lake is impaired for nutrients.
| Landcover Type | O’Connors Creek |
| Agriculture | 67% |
| Forest | 6% |
| Grassland | 16% |
| Shrubland | 1.5% |
| Urban | 9% |
| Water | 1% |
What is an impaired waterbody?
A waterbody is considered “impaired” if it doesn’t meet one or more water quality standards. In Minnesota, water quality standards protect lakes, rivers, streams, and wetlands by defining how much of a pollutant can be in the water before it is no longer drinkable, swimmable, fishable, or otherwise usable.
Types of Water Impairments:
- Mercury – High levels lead to fish consumption advisories
- Nutrients – Such as phosphorus and nitrogen, which cause algae blooms
- Sediment – Sediment-heavy water is known as turbid, and restricts the light needed for aquatic life
- Bacteria – Water can become unsafe for swimming if contaminated with bacteria such as E.Coli
- Unhealthy Conditions – Fish and macroinvertebrates are essential to a healthy aquatic system; a waterbody can become unhealthy to the point of impairment
- PFOS & PFAS – High levels of perfluorooctane sulfonate (PFOS) and polyfluoroalkyl substances (PFAS)
- Sulfate – A waterbody impaired for sulfates harms the biological production of wild rice
Monitoring Data
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