The Lonja is a river in central Croatia, a left tributary of the Sava. It is 49 kilometres long and its basin covers an area of 4,259 square kilometres. The Lonja rises in the Kalnik mountain in northern Croatia, southeast of Novi Marof, at 46°07′57″N 16°22′17″E / 46.132404°N 16.371417°E. It flows westward until turning south near Breznički Hum, passing east …The Lonja is a river in central Croatia, a left tributary of the Sava. It is 49 kilometres long and its basin covers an area of 4,259 square kilometres. The Lonja rises in the Kalnik mountain in northern Croatia, southeast of Novi Marof, at 46°07′57″N 16°22′17″E / 46.132404°N 16.371417°E. It flows westward until turning south near Breznički Hum, passing east of Sveti Ivan Zelina, and turning southeast near Sveta Helena. East of Lupoglav, it turns south again, passing through Ivanić-Grad and nearing the river Sava.