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Reshanau Lake Management Plan • IV. History /Summary of Existing Data Reshanau Lake was formed by dredging the swampy area, roughly where the lake now exist, in the late 1960's and early 1970's. The material removed from the lake was used to make what is now Chomonix Golf course and to make build able lots on the lake's perimeter. For a number of years, the lake was treated annually by a commercial applier but was discontinued for some reason before 1995. Over the years individual property owners have applied some chemical treatments with marginal or no apparent success. Attempts have been made over the years to form an Association of property owners but have been unsuccessful. In 1995 a study of Reshanau Lake was conducted by Montgomery Watson (Attachment A), which provides some historical and benchmark data. This report shows that Reshanau Lake is Eutrophic (high in nutrients) and does not support swimming or other contact water activity according to Minnesota Pollution Control Agency (MPCA) standards. The report also suggests that the growth of the exotic curly -leaf pondweed contributes significant phosphorus to the lake. A summary of the 1995 lake monitoring report shows that the in -lake total phosphorus (TP) levels averaged 110 ug /L during the growing season. TP is the nutrient that drives algal productivity in most northern latitude states. This nutrient is generally the limiting factor for plant growth. Since this nutrient is often associated with man induced activities, it is almost always the nutrient that lake managers target to reduce the frequency and duration of algae blooms and to help control SAV growth. TP entering the lake is coming from four primary sources. Theses sources are County Ditch 25 (CD25) which enters on the east side of the lake, a small tributary creek which enters the lake on the south side, internal cycling of TP from the die off and decomposition of curlyleaf pondweed, and direct drainage from manicured lawn runoff and possible failing septic tanks. The early summer TP levels are 70 pg /L and peak at 140 µg /L in late July. This peak TP concentration coincides with the die -off and decomposition of curlyleaf pondweed in the lake. Looking back at the 1995 stream monitoring data also suggests that during the flashier stream flow period of July and August TP export from CD 25 is higher. The Chlorophyll -a (CHLA) concentration averaged 3911g /L during the growing season and was at a low of 11 p.g /L in early June and peaked at 121 µg /L in early August. CHLA measurement is a measurement of plant productivity in a lake. All vascular plants produce CHLA and this measurement is related to the amount of algae when a surface water sample is collected and analyzed. CHLA concentrations generally increase with an increase in TP concentrations. The CHLA cycle is also attributable to the die -off and G: \Admin \Board \Agenda Paks \2005 Agenda Paks \2005 -04 -13 \Reshanau mgmt plan.doc4