Int. J. Environ. Res. Public Health 2009, 6 179 Figure 2. LANDSAT image from 1986 showing the location of different Mayak reservoirs. The blue line through Reservoir 11 traces the original bed of the River Techa before dam 11 was constructed. Lake Karachay is indicated as Reservoir 9 (R9). 1.3. Radiation Affected Populations Population groups exposed to radioactive contamination due to the Mayak PA operations include: (1) The workforce at the Mayak PA (2) Participants in clean-up work carried out after the accidental releases in the Urals (3) Local residents around the Mayak PA who were exposed due to environmental discharges of radioactivity and/or radiation accidents Members of the third group (offsite population) are the focus of this article and have been subject to detailed studies where personal data on health status in the riverside population groups have been gathered in a registry, the Techa River Cohort. Highest radiation doses were received by residents in riverside villages along the Techa (28,000 people [15]) and those within the initial deposition area of the EURT. The population exposed to Techa River contamination resided in four rural administrative districts (two in the Chelyabinsk and Kurgan Regions, respectively) and consisted of ethnic Russians [Slavic], Tartars and Bashkirs [Asiatic]; Tartars and Bashkirs constituted 24 % of the total exposed population. In 1950, 41 villages (total population: 23,500) were located downstream from Mayak PA when the main discharges occurred. The majority of the settlements were small with less than 500 inhabitants [16]. Four inhabited settlements remain on the Techa River in the Chelyabinsk region, these being (in order of proximity to the Mayak PA): Muslyumovo, Brodokalmak, Russkaya Techa and N. Petropavlovskoye with a total population of 9,229 persons as of the census of 1989 [17]. Of the