In 2010–2012, the hydrogeological model (HM) of Latvia (LAMO) was established by the scientists of Riga Technical University (RTU). In 2013–2014, LAMO was upgraded. In 2015, the recent version LAMO4 was developed. In LAMO4, the plane approximation step was decreased from 500 meters to 250 meters. The baseflows of rivers for HM were adjusted by accounting for data that were provided by the measurements of river streams. LAMO is run by the licensed program Groundwater Vistas (GV), version 6. It contains the MODFOW and MODPATH programs for supporting HM and for tracking groundwater particles, respectively. By using MODPATH, the case of the Iecava river was investigated, in order to find the sources that support groundwater inflow into the river (its baseflow). Unforeseen results were obtained. Due to the appliance of LAMO4, it was discovered that some part of the river baseflow comes from the areas that are located very far from the river drainage basin. It also was not expected that even within the basin, the particle traces were very complex. The results described in the paper serve as demonstration for the usefulness of applying a large complex HM for investigating the processes of nature.