This database is from a short-term research study designed to assess the effect of application of low doses of the herbicide fluridone (Sonar®) on Eurasian watermilfoil (EWM), other plant species, and water quality in lakes in 7 lakes in southern Michigan. Low doses of fluridone are expected to only impact EWM and not the rest of the plant community. Three of the lakes had no herbicide treatment done on them (Big Seven, Clear and Heron), three of the lakes had treatment done on them such that EWM decreased in the lake during treatment years (Big Crooked, Camp, and Lobdell); and one lake had treatment that was unsuccessful in changing the plant community (Wolverine). Treatment was done in 1998 during the first year of water chemistry sampling. The plant community did not change drastically, and so treatment did not affect water quality (Bremigan et al. 2005). The responses of aquatic invertebrates (Cheruvelil et al 2000, Cheruvelil et al. 2002) and fish (Valley and Bremigan 2002a,b) were also assessed.