The Shagan river is the only surface waterway on the SNTS territory. It flows along the eastern boundary of the SNTS and is a left-bank tributary of the Irtysh river. The length of the Shagan riverbed is 275 km with an average slope 0.003, which changes considerably from one part of the riverbed to the other. Within the Balapan testing ground the length of the riverbed is about 50 km, and the slope angle is, on average, 0.002. The watershed area of the left-bank part of the testing ground, where testing wells are located, is about 900 km2.
In 2006 during radio-ecologcal investigations of the SNTS aquatic environment, scientists determined contamination of the Shagan river with radioactive products of nuclear explosions. The main radioactive pollutant is tritium. Maximal tritium concentration in the river waters (40*104 Bq/l) was registered 4.7 km away from the Atomic lake at levels of more than 50 times higher than the maximal permissible level for drinking water. As the distance from the Atomic lake increases, tritium concentration in the Shagan waters considerably decreases, and in the place of its confluence with the Irtysh river tritium concentration in water becomes 10 Bq/l, which is equal to MPL (maximal permissible level) used for equipment. A complex of scientific investigations including hydrogeological, hydrological and geophysical investigations showed that tritium contamination of the Shagan waters is caused by the discharge of contaminated ground waters from the testing ground Balapan.
In 2007 additional investigations of the river ecosystem showed that surface waters of the river in addition to tritium contained 90Sr, and bottom sedimentations were contaminated with 60Co, 152Eu, 154Eu and 137Cs. It should be noted that concentration of 90Sr in water reaches the level comparable with intervention level established by NRB-99, (for water and food intake). By the character of tritium and 90Sr distribution in water, it was established that the radionuclides have absolutely different sources. Whereas the nature of tritium presence in the water is quite understandable, the source of 90Sr has not been studied yet. To determine the reasons for noticeable increase of the 90Sr concentration in water and the ways of its proliferation into the river, additional investigations are necessary. Possible mechanisms for 90Sr proliferation into the river may be its inflow with ground waters, plane washing off, washing out of 90Sr from contaminated man-made soils of Atomic lake by atmospheric precipitations.