The Krupa river is the Neretva left tributary and the main water current of Hutovo Blato, which leads the waters from Gornje Blato and Svitavsko lake into the Neretva river. The length of Krupa is 9 km with an average depth of 5 meters. Krupa does not have an actual source, but is actually an arm of Deransko lake. Also, the Krupa is a unique river in Europe, because the river flows both ways. It flows 'normally' from the 'source' to the mouth and from the mouth to the 'source'. This happens when, due to high water level and large quantity of water, river Neretva pushes the Krupa river in opposite direction .
Neretva (Italian: Narenta, pronounced [nɛ̌rɛtʋa]) is the largest river of the eastern part of the Adriatic basin. Four HE power-plants with large dams (higher than 15 metres) provide flood protection, power and water storage. It is still recognized for its natural beauty and diversity of its landscape.
Freshwater ecosystems have suffered from an increasing population and the associated development pressures. One of the most valuable natural resources of Bosnia and Herzegovina and Croatia is its freshwater resource, contained by an abundant wellspring and clear rivers. Situated between the major regional rivers (Drina river on the east, Una river on the west and the Sava river) the Neretva basin contains the most significant source of drinking water.
The Neretva is notable among rivers of the Dinaric Alps region, especially regarding its diverse ecosystems and habitats, flora and fauna, cultural and historic heritage.
The Neretva flows through Bosnia and Herzegovina and Croatia and is the largest karst river in the Dinaric Alps in the eastern part of the Adriatic basin/watershed. Its total length is 230 kilometres (143 miles), of which 208 kilometres (129 miles) are in Bosnia and Herzegovina, while the final 22 kilometres (14 miles) are in the Dubrovnik-Neretva County of Croatia.