The Paraná River forms part of the border between which countries?

Which river flows through both Poland and Germany? What is the name of the river that crosses the border of Costa Rica and Nicaragua? Which river forms part of the border between Brazil and Peru? The Kosi River flows through which countries? The Tigris River flows through which countries? The Okavango River flows through which countries? The Indus River flows through which countries? The Niger River flows through which countries?