07/31/2008 Env Bd Packet - Laserfiche WebLink

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MEMORANDUM Rice Creek Watershed District To: Marty Asleson From: Matthew Kocian (763- 398 -3075) Subject: Reshanau Lake — Curlyleaf Pondweed Control Date: 7/21/2008 Background / Discussion Reshanau Lake, located in Lino Lakes, MN, supports a substantial population of curlyleaf pondweed (Potamogeton crispus). Curlyleaf pondweed is a non - native plant species that is characterized by its unusual life - cycle. The submerged plant begins growing while ice is still present on lakes. It dies around mid- summer, at which time the plant decomposes in the water column. It can grow in dense stands, often outcompeting native plants. In cases where the density is very high, as in Reshanau Lake, the decomposition of the plant material at mid - summer releases significant amounts of phosphorus. Excess phosphorus fuels algal growth and can result in poor water clarity. Dense curlyleaf populations can also inhibit recreation by forming surface mats. Aquatic vegetation surveys in Reshanau Lake have found curlyleaf present at roughly 95% of survey sites, and at all depths. Many sites exhibited high curlyleaf density. Very little native aquatic vegetation was found during surveys. Ongoing Control Herbicides have been used to control curlyleaf pondweed in Reshanau Lake since 2005. Treatments have been effective at controlling curlyleaf; each of the 130 monitoring stations does not support curlyleaf after herbicide treatment. In 2008, the cost of the chemical treatment was $35, 814. The cost of the treatment was split 50/50 between the Rice Creek Watershed District and residents of Reshanau Lake. The vendor responsible for the treatment has warned of future price increases, as demand for the chemical increases. • •