Armstrong Lake
Armstrong Lake
Lake Description
Armstrong Lake is located at the north end of the watershed district in Lake Elmo and Oakdale. The lake is made up of a northern and southern portion located across the two cities and split by Highway 10. Armstrong Lake acts as the headwaters of a multi-lake system, which outlets to multiple small wetlands and eventually to Wilmes Lake north basin.
Lake Details
| Location | Lake Elmo, Oakdale |
| Shallow/Deep | Shallow |
| Surface Area | 29 acres |
| Maximum Depth | 1.5 meters |
| Impairment Status | Not listed |
| Downstream Waterbody | Wilmes Lake North Basin |
| DNR FiN Lake | No |
Monitoring & Water Quality in Armstrong Lake
Armstrong Lake is a shallow lake with a maximum depth of 1.5 meters, and the lake is 29-acres in size. The lake’s watershed is 563 acres, with 191 acres of impervious surface from residential and commercial land use. Average Secchi depth in Armstrong Lake is 0.9 meters, which is just below the Minnesota State Standard of 1.0 meters. A Secchi disk is a black and white circular disk used to measure water transparency or turbidity by assessing the depth the disk is visually present under the surface of the water. The more turbid or “murky” the water, the shallower the Secchi depth will be, the more transparent or “clear” the water, the deeper the Secchi depth will be.
On average, the Total Phosphorus (TP) concentration in Armstrong lake exceeds the shallow lake standard (60 μg/L).
Monitoring Data
Armstrong Lake Vegetation
Armstrong Lake is seasonally monitored and surveyed for aquatic vegetation, and water quality metrics which are reported in the annual Aquatic Vegetation Report.
Vegetation in Armstrong Lake historically consists of dense cattail and invasive white and native yellow water lilies. It is also common to find Common Coontail (Ceratophyllum demersum), and other submersed vegetation, which can make lake navigation difficult. Armstrong Lake is not managed for aquatic invasive species (AIS).
One way to measure lake health is by species richness, or the presence or lack of a diverse aquatic animal population. In general, Armstrong Lake has average species richness, but is above average for a lake of its size. Since 2015, the lake has maintained the same level of species diversity and has even improved, with recent surveys indicating high biological integrity.
Cattail Harvesting
In 2025, SWWD launched a the cattail harvest pilot project at Armstrong Lake. The project tested whether removing invasive hybrid cattails (Typha × glauca) from the large wetland upstream of the lake could provide a practical, cost-effective way to remove phosphorus, chloride, and other pollutants from the watershed.
The pilot produced promising results. Harvesting approximately 0.4 acres of cattails removed up to 28 pounds of phosphorus and approximately 352 pounds of chloride from the wetland system.
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