of reedbebds and trees. It represents a more interesting preserved area. Krupa River The Krupa River is a Neretva left tributary and the main water current of Hutovo Blato, which carries the waters from Gornje Blato and Svitavsko Lake into the Neretva River. The length of Krupa is with an average depth of . The Krupa does not have a specific source, but is an arm of Deransko Lake. Also, the Krupa is a unique river in Europe, because it flows both ways. It flows both towards and back from its mouth. This happens when a high water level causes Neretva to push Krupa in the opposite direction. Neretva Delta wetlands Passing towns and villages in Bosnia and Herzegovina, the Neretva spills out into the Adriatic Sea, building a wetland delta that is listed under the Ramsar Convention as internationally important. In this lower alluvial valley in Croatia, the Neretva River splinters into multiple courses, creating a delta covering approximately 12,000 hectares. The delta in Croatia has been reduced by extensive land reclamation projects, reducing the river flows to just three branches from the original twelve. The marshes, lagoons and lakes that once dotted this plain have disappeared and only fragments of the old Mediterranean wetlands survive. Wetlands, marshes and lagoons, lakes, beaches, rivers, hummocks (limestone hills) and mountains compose the delta, with five protected areas with a total area of 1,620 ha. These are ornithological, ichthyologic and landscape reserves. Endemic and endangered species Dinaric karst water systems support 25% of the total of 546 fish species in Europe, many endemic. The Neretva River, together with four other areas in the Mediterranean, has the largest number of threatened freshwater fish species. The degree of endemism in the karst ecoregion is greater than 10%. Multiple fish species have small habitats and are vulnerable, so they are included on the Red List of endangered fish . The Adriatic basin has 88 species of fish, of which 44 are Mediterranean endemic species, and 41 are Adriatic endemic species. More than half of the Adriatic river basin species of fish inhabit the Neretva, the Ombla, the Trebišnjica, the Morača Rivers and their tributaries, and more than 30 are endemic. Invasive species A pike perch (Sander lucioperca Linnaeus 1758) (also see Sander (genus)) population in the Neretva River watershed was observed in 1990 for the first time. The Rama River, a right tributary of the