The Neretva (pronounced [něreːtʋa], Serbian Cyrillic: Неретва), also known as Narenta, is one of the largest rivers of the eastern part of the Adriatic basin. Four hydroelectric power plants with large dams (higher than 15 metres) provide flood protection, electricity and water storage. The Neretva is recognized for its natural environment and diverse landscapes.

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.

Its name has been suggested to come from the Indo-European root *ner, meaning "to dive". The same root is seen in the Serbo-Croatian root "roniti".

The Neretva flows through Bosnia and Herzegovina and Croatia before reaching the Adriatic Sea. It is the largest karst river in the Dinaric Alps in the eastern part of the Adriatic basin/watershed. Its total length is 225 kilometres (140 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.

The Neretva watershed is 11,798 square kilometres (4,555 sq mi) in total; in Bosnia and Herzegovina 11,368 square kilometres (4,389 sq mi) with the addition of the Trebišnjica river watershed and in Croatia, 430 square kilometres (170 sq mi). The average discharge at profile Žitomislići in Bosnia and Herzegovina is 233 cubic metres per second (8,200 cu ft/s) and at the mouth in Croatia is 341 cubic metres per second (12,000 cu ft/s) in addition to the Trebišnjica River's 402 cubic metres per second (14,200 cu ft/s). The Trebišnjica River basin is included in the Neretva watershed due to a physical link of the two basins by the porous karst terrain.

The hydrological parameters of Neretva are regularly monitored in Croatia at Metković.

Geographically and hydrologically the Neretva is divided into three sections.