Usually in case of Bengali , Hindi , Persian etc. the masculine word is a-karanta and the feminine word is a-karanta or e , e-karanta. For example: river-river , Kumar-Kumari etc. So all the rivers whose names are masculine are followed by 'rivers' (eg: Kopotaksh river , Brahmaputra river , Nile river etc.) and all rivers whose names are feminine are followed by 'rivers' (eg Padma river , Jamuna river etc.).