Aquatic Plant Management in the District
A healthy and diverse population of native aquatic plants is essential to good water quality and a healthy lake. Responsible for protecting that population, the MN DNR carefully regulates activities that may threaten it. Generally, control/removal of native emergent plants (bulrush and cattails) is not allowed; native submergent plants can be removed when interference with recreation or navigation can be shown. However, for the last several years, the District’s vegetation problems center around Flowering Rush and Curly-leafed pondweed, which are both invasive species that require management.
Aquatic plant harvesting hs been a very important activity for the District, and has consumed a significant amount of time and resources throughout its history. Within a few months of the inception of the District, a petition from Melissa-Sallie residents called for establishment of a project to remove lake weeds. It was conventional wisdom among limnologists of the time that the most practical way of reducing nutrient levels in lakes was to remove plant material (which contains large quantities of nutrients). Indeed, the 1967 Overall Plan prominently featured mechanical removal of excess aquatic plants as a means to address lake "eutrophication". In 1968, the District established the first three projects aimed at removing aquatic plant material from Sallie and Melissa. Originally funded in large part by grant money and donations from the City, County and lake associations. Project 1 operated off and on until 1978. It was succeeded by Project 1A in 1978 and 1B in 1985; successor projects relied heavily upon donations from the District general fund, as well as direct assessment to affected lakeshore property owners.
After several years of systematic evaluation which received national attention from limnologists, research by Dr. Joe Neel (UND) concluded that significant nutrient reduction could not be brought about by harvesting. In the early 1970's the District shifted its harvesting emphasis towards reducing aquatic plants in order to enhance boating and swimming. A Detroit harvesting project (1C) was established in 1990, with the added control of the exotic plant, Flowering Rush, to its project purpose.
The project continued to harvest Curly-leaf Pondweed through 2014. Beginning in 2003, the District began experimenting with herbicides to control Flowering Rush under the auspices of the Harvesting projects. In 2013, after protracted negotiations with the DNR, and elaborate research efforts by national experts and the Army Corps of Engineers, the District began aggressive control measures using the herbicide Diquat. Control efforts have been widely seen as successful. after successful reductions in plant biomass an adaptive approach was developed to allow annual treatment to maintain a low population density.
In 2016 and 2017, the District also chemically treated Curlyleafed pondweed on Lakes Detroit, Curfman, Sallie and Melissa. The plant reductions have been so great with the chemical treatments that the District Managers felt confident enough to sale the last aquatic harvester, thus moving the District into a new era of lake plant management.
District staff harvested Curlyleaf Pondweed on Big Detroit up to 2014. The harvesters have now been sold.
Flowering Rush Infestation on Big Detroit Lake in 2007.
View the Districts Aquatic Plant Management Plan HERE
Read the Change in Direction Paper HERE
Photographic Comparisons of Flowering Rush Infestations