GUWAHATI: The Pollution Control Board, Assam (PCBA) has started a collection of river water samples so as to ascertain the impact of the COVID-19 lockdown. The PCBA has started the move from Sunday. It will collect as many as 101 samples from the rivers in the State and conduct tests to ascertain the level of pollutions. Following the COVID-19 lockdown, it is assumed that the pollution levels of the rivers in the State may show improvement. However, similar tests by the PCBA on air pollution do not show any improvement.