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Figure 1. Lake Minnetonka., Minnesota. Locations one through five were experimental plot sites. Location six is the first area milfoil was found in Lake Minnetonka <br />Harvesting took place on July 3, 1990, in the middle of <br />the growing season, after milfoil had reached peak biomass. <br />At each site a mechanical harvester cut a path 4.9 meters <br />wide from the off shore weed line to the inshore weed line <br />along a predetermined path. Following harvest an 18 meter <br />by 3 meter plot was delineated with buoys. Reference plots of <br />TABLE 1. WATER CLARITY AND PERCENT ORGANIC MATTER IN THE SEDIMENTS. <br />SITES SHARING THE SAME LETTER ARE NOT SIGNIFICANTLY DIFFERENT (P.0.05) . <br />Location Secchi depth' (m) Percent organic matter in <br />sediments' <br />Shady Island 2.Oa 6.0 a <br />Crystal Bay <br />1.6 b <br />3.1 b <br />Hardscrabble Point <br />1.35 c <br />1.6 c <br />North Arm <br />1.3 c <br />1.5 c <br />Maxwell Bay <br />1.2s <br />1.3 c <br />'Each value is a mean of 27 samples or measurements. <br />equal area were marked adjacent to each treatment plot on a <br />random side. Each plot was subdivided into three equal <br />areas; "near shore", "mid -area", and "furthest from shore". <br />Three biomass samples were taken in each subdivision each <br />week for 9 weeks following harvest (except for the 1st week <br />when only 2 samples were taken). <br />SAMPLING METHODS <br />Density of the vegetation precluded SCUBA sampling for <br />biomass. Thus we sampled with a rake, with a 3 meter <br />extending to 5 meter handle, which was lowered to the sedi- <br />ment surface and rotated 360 degrees. The 0.15 In wide rake <br />sampled 0.02 m2 area. To test accuracy and precision of this <br />method, samples were taken at two sites in Lake Minnetonka <br />during the summer of 1991 using both 0.0625 m2SCUBA <br />quadrats and the rake and compared using analysis of vari- <br />ance and coefficients of variation. Results show that while the <br />rake method gave larger estimates of biomass than the quad - <br />J. Aquat. Plant Manage. 32: 1994. 57 <br />