4.5. SR 10-20-2003 - Laserfiche WebLink

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Item 4.5. City TO: FROM: DATE: SUBJECT: MEMORANDUM Mayor and City Council Stephen Rohlf, Building and Environmental Administrator October 20, 2003 ~ Consider Curlyleaf Pond Weed Remediation in Lake Orono Curlyleaf Pond Weed, a non native invasive aquatic plant, was first discovered in Lake Orono last year. A survey of the lake this year revealed an alarming increase of this plant. Left unchecked, this weed will totally clog shallow areas of waterways, which in Lake Orono, is most of the lake. Potential remediafion measures for this problem include mechanical harvesting, herbicide and freezing the plant out. Members of the Lake Orono Improvement Association and city staff met with representatives from the Minnesota Department of Natural Resources (DNR) Division of Waters, Fisheries and Aquatic Plants on October 8, 2003 regarding what to do about Curlyleaf Pond Weed in the lake. Staff is recommending the city do this third option (freeze it out). What is involved is a gradual four foot draw down of the lake (approximately over a one week period), allowing the lake sediment to dry (approximately one week depending on weather) and having cold enough temperatures to freeze the plant bulbs that are contained in the sediment of the lake (approximately ten days). Drawing the lake down four feet will eradicate the majority of the Curlyleaf Pond Weed, if temperatures are cold enough, while still retaining enough water depth to avoid a fish kill. DNR Fisheries will determine when the lake has to be refilled, even if weather conditions are not favorable for success. The concern is having lake level back up before it gets too cold and oxygen starts to deplete in the water. Staff still needs to talk to the Elk River Municipal Utilities regarding the project. A potential issue is having the gates for the dam freeze open, making it impossible to refill the lake, prior to spring thaw. Staff will have an answer to this question for Monday night's meeting. Staff will also have more certain dates for when a draw down of the lake would take place, but it is most likely that it will occur in mid November. The cost for this remediafion is $0.