Lake Owasso hosts a variety of aquatic plants, both native and non-native invasive species. The two primary invasive species on Lake Owasso – curly leaf pondweed, and eurasian water milfoil – are primary targets for annual treatment applications. Experts maintain a healthy lake hosts a diversity of plant species – ideally mostly natives. An overabundance of invasive species have at least two negative effects 1) native species tend to get drown out, and 2) the resulting plant base becomes less diverse. Eurasian milfoil was first discovered on Lake Owasso in June of 2000 and in 2023 Eurasion milfoil was so bad that a special treatment using flouridone was conducted in 2024. There is no known record of the introduction date of curly leaf pondweed on Lake Owasso; however, it is known that curly leaf pond weed was first found in North America in the 1880’s where it is native to Eurasia, Africa, and Australia. While fully eradicating a particular plant is not feasible, eurasian water milfoil (per the annual treatment program) has been largely held in check since June of 2000.
Major aquatic plant categories
Eurasion Water Milfoil vs Large Leaf Pondweed
In 2025, native aquatic vegetation, previously unable to compete with EWM (pre-flouridone), expanded in frequency. While native aquatic vegetation may interfere with recreation, most common species do not form dense surface mats. Relief from native vegetation can most often be addressed with individual shoreline controls. Unlike many lakes with widespread EWM growth, Lake Owasso continues to have a diverse population of native aquatic species.
Large-leaf pondweed saw the greatest increase in 2025. This was a similar occurrence in neighboring lakes, including Lake Josephine. It is assumed ideal conditions and lack of competition allowed for significant expansion in 2025. Flatstem pondweed (also a native) increased significantly, but also does not surface mat and thus does not pose a navigational hinderance like EWM. Also most flatstem pondweed is located in the central portion of the lake where the treatment allowance is less. Other native species (elodea, naiad, etc.) saw more limited expansion of frequency and density.
The LLP EWM Trade-off
| LLP | EWM |
| Does not mat at the surface (less restrictive on propellers than EWM). | Mats at the surface (navigational challenge for propellers). |
| With no surface mat, algae does not agglomerate with LLP. (LLP does have a single stem that pokes through the surface but where no horizonal growth (surface matting occurs). | EWM Mats are so dense they also serve as agglomeration sites. Filamentous algae (the dark green stringy and slimy material, which otherwise sinks to the lake bottom) agglomerates on top of EWM, making the EWM matting even worse, including a stench. |
| LLP is not an impediment to circulation. Waves pass right through LLP patches where ample circulation still occurs. | EWM patches are so dense that waves do not thoroughly pass through them, thereby cutting down on a natural healthy circulation of water. |
| Subsurface open architecture (less propeller restriction than EWM). | Densely packed stems below the surface (pontoons can get stuck in a dense patch.) |
| Native Present in Minnesota lakes for thousands of years (some claim since shortly after the last ice age). | Invasive (newly introduced on Owasso in 2000.EWM outcompetes natives. |
Other benefits of Large Leaf Pondweed
| LLP is among the least oxygen depleting submerged aquatic plants. Other aquatic plants deplete oxygen more quickly; causing subsequent problems for fish and waterfowl habitat, and increased algae blooms. |
| LLP beds provide excellent habitat for loons. Loons often dwell adjacent to LLP beds given their abundance of prey (juvenile bluegills and perch). |
| LLP is a most favored habitat for Walleye. |
| LLP is effective at absorbing phosphorus and nitrogen where such nutrients can otherwise result in cloudier water (a green lake). Some lakes that become too cloudy lose their loon families to lakes with better water clarity. |
| The presence of LLP has a deterrent effect on the re-emergence of EWM |