Rivers are the major transporting means for dissolved and particulate matter from the continents into the seas and lakes (Meybeck, 1988). Dissolved metals come into the particulate phase due to flocculation processes during estuarine mixing (Eckert and Sholkovitz, 1976; Sholkovitz, et al., 1977 and Boyle, et al., 1977). Many investigations have been carried out on flocculation of dissolved substances to know about the controlling mechanisms. In wetlands, flocculation is enhanced by increased pH, turbulence, concentration of suspended matters, ionic strength and high algal concentration (Matagi, et al., 1998). However not much information is available on recognition of dissolved metals flocculation processes during estuarine mixing of river waters with brackish lake waters such as the Caspian Sea water (Karbassi and Nadjafpour, 1996 and Saeedi, et al., 2003). These investigations seem to be one of a few studies of the sort carried out in the southern coasts of the largest lake in the world – the Caspian Sea. It should be pointed out that other researchers have mainly focused on colloidal stability, surface properties, humic acids, salinity and pH (Zhiqing, et al., 1987; Hunterm, 1983 Featherstone and O’Grady, 1997; Karbassi, 1989 and Shankar and Karbassi, 1992). In the present study, flocculation of Cu, Mn, Ni, Zn and Pb during mixing of Talar of river waters with the Caspian Sea waters in relation to the various important sea water parameters such as Ec, pH, salinity, total organic carbon, NO3, and SO4 is investigated. The Caspian Sea covers an area of about 371000 km2 that lies between the Caucasus Mountains and northern Iran. The salinity of Caspian Sea waters ranges from 4 ppt in the northern parts to almost 13% in the southern parts.