Agenda - Environmental Policy Board - 10/17/2016

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The reason for the explosion in aquatic plant growth is not clear. While plant growth is expected to increase with clearer water,there were no changes in the watershed or lake management that would have created clearer water. The abundant plant species in Rogers Lake are not generally aggressive or problematic in other lakes. Low water levels,cooler than usual spring weather in consecutive years, and past illegal herbicide treatments are possible reasons for vegetation changes in the lake. While some plant management may be beneficial for this lake,little is legally allowed. A purpose of plant management would be to reduce spring plant growth as a way of reducing the amount of decaying plant material later in summer. This should result in higher summer dissolved oxygen. It will also increase open water areas for recreation, such as canoeing. It should not be designed to eliminate plants;plants are essential to the health of shallow lakes. Generally less no more than 15% of the lake should be treated and treatment should be targeted toward critical species and areas. Little vegetation management is legal on Rogers Lake for the following reasons: • Rogers Lake is classified as a natural environment lake, and no herbicide use is allowed under state rules. Mechanical clearing of an area up to 2500 square feet per property is allowed without a permit. • Where floating leaf vegetation(lilies,water shield)is present,only mechanical clearing of a 15 foot wide channel to open water is allowed without a permit. There is no open water to try to reach. Lilies and water shield are almost everywhere on Rogers Lake,eliminating almost all allowable vegetation clearing. Obtaining a permit for greater areas is possible. • State rules discourage vegetation control on shallow lakes,which are healthiest when plant-dominated. • Invasive species are not a problem. Vegetation control is generally not allowed or discouraged for native species that are most abunant on Rogers Lake. • Overriding the noted problems about low dissolved oxygen and open water for recreation are the fact that there should be little expectation for a fishery or open water recreation on such a shallow lake. In summary,the only allowable vegetation clearing on Rogers Lake is (a)mechanical clearing of an area 2500 square feet in the rare instances where no floating leaf vegetation would be impacted and(b) a 15 foot channel where floating leaf plants are present. Residents may apply for a permit for greater areas. See the DNR website or publications for more detailed information on state aquatic vegetation rules before proceeding with any work. In the end,the current plant-dominated condition of Rogers Lake should be adopted as the best condition for this lake. Ecologically, a shallow lake of this type is healthiest when it is plant dominated. State water quality standards and state plant management rules are designed to promote this condition. Admittedly, for Rogers Lake there is a negative side—reduced recreational suitability and reduced dissolved oxygen. These conditions are common for this type of lake in a healthy condition. Aerial photos showing increase in aquatic plants,particularly between 2006 and 2008. Light green areas are aquatic plants. Black areas are o en water. 4 AiWL 2000 2003 2006 2008