During our research (Brakovska & Skute, 2007, 2009; Brakovska & Paidere, 2012; Brakovska et al.
Lake Dridzis is the deepest lake in Latvia as well as in the Baltic countries (Brakovska & Skute, 2007; www.
Besides, the surroundings of Lake Rica are a complex protected area of landscape and an area of Natura 2000 (Tidrikis, 1997; Brakovska & Skute, 2007).
For identification we used the following zooplankton guides: Manujlova, 1964; Kutikova, 1970; Flossner, 1972, 2002; Pontin, 1978; Sloka, 1981; Krauter & Streble, 1988; Scourfield & Harding, 1994; Segers, 1995; Dussart & Defaye, 2001; Dumont & Negrea, 2002; Nogrady & Segers, 2002; and Paidere & Skute, 2011.
In comparison with the surveys carried out in previous years (Brakovska & Skute, 2007, 2009), the composition of Cladocera species and physico-chemical parameters of water had not changed significantly.
In general, analysis of Cladocera species in the pelagic zones of lakes Svente, Rica, Dridzis, and Geranimovas-Ilzas in July 2010 and July 2011 did not reveal significant differences in the qualitative and quantitative composition of species in comparison with earlier studies (Brakovska & Skute, 2007, 2009; Brakovska & Paidere, 2012; Brakovska et al.