The long-term dynamics of suspended matter in the Naroch lakes has been analyzed with the help of autoregressive integrated moving average (ARIMA) models. A comparison of the models showed that, apart from seasonal fluctuations, all Naroch lakes have been affected by dramatic impact, which has resulted in a rapid decrease in absolute values and fluctuation decrease of seston concentration. The models indicate that, in contrast to lakes Naroch and Myastro, the dynamics of the seston concentration in Lake Batorino is characterized by a longer period of stabilization after the impact that occurred in 1991.