Hydrogeological model (HM) of Latvia (LAMO) is used for simulation of groundwater flow regime in its active zone. Surface waters – rivers, lakes and sea have great influence on groundwater flow. Current LAMO3 version contains 27 layers with 610 x 951 x 27 = 15 431 877 spatial grid nodes; the plane approximation step of LAMO3 is 500 meters. Rivers, lakes and sea form hydrographical network (HN) of LAMO3: 462 rivers in 42 680 nodes and 128 lakes and sea in 104303 nodes are attached to aquifers. Development, modifying and improving of HN is an iterative process. Adding or excluding of a particular river or lake must be performed in short time. It is impossible to do it without developing special software, which performs automation of creating the HN and including it into the model. This paper describes some algorithms and software, which were used for HN creation and its inclusion into LAMO3, such as the data interpolation of river and lake geometry, attaching HN to the model, immersion of river valleys into the HM body, creation of HN data for a model version with a different plane approximation step, joining of model surfaces for data input for Groundwater Vistas (GV) modelling system and software solution overview, which achieved all objectives of HN creation.