Investigators in 1951 found communities along the river highly contaminated. On discovery, soldiers immediately evacuated the first downriver village of Metlino, population 1,200, where radiation levels measured 3.5–5 rads/hr (35–50 mGy/hr or 10–14 μGy/s). At that dose, people could get a lifetime external dose in less than a week. During the following decade, ten additional communities were resettled from the river, but the largest community, Muslumovo, remained. Researchers investigated residents of Muslumovo annually in what has become a four-generation living experiment of people living among chronic, low doses of radioactivity. Blood samples showed its villagers took in caesium-137, ruthenium-106, strontium-90, and iodine-131, internally and externally. These isotopes had deposited in organs, flesh and bone marrow. Villagers complained of a range of illnesses and symptoms—chronic fatigue, sleep and fertility problems, weight loss and increased hypertension. The frequency of birth defects and complications at birth were up to three times greater than normal. In 1953, doctors examined 587 of 28,000 exposed people and found that 200 had clear cases of radiation poisoning.