The river is 61 km long and although before the construction of hydroelectric power was as much as 100 kilometers long. It stretches from its source Tonkovic vrilo and slowly down the field area Gacko receiving numerous tributaries. It features her clear pure water that despite the rocky end of the relatively slow flow. The average summer temperature is 10.8 ° and 7.9 ° in the winter. The river depth varies from one meter up to 10 meters at the deepest parts. By its chemical composition, the water is quite hard, slightly alkaline and rich in calcium salts which promotes the growth of vegetation around the river and is rich in oxygen. From 9.1 to 13.5 mg / L. The bottom of the river is muddy. Gacka river abounds in underwater caves and springs sites. The first study began in the second half of the twentieth century, but until then, the underwater world Gacka was a complete mystery. Majerovo spring is considered the richest Caves, and in the recent time its devoted special attention. It is believed that over half of underwater passages and channels Gacka is still unexplored.  

Tourism and fishing

The development of tourism began in the second half of the twentieth century when the construction of tourist facilities in the Gacka and surrounding areas. A large contribution to the popularity of Gacka are given and the Plitvice Lakes, because a large number of tourists traveling to Plitvice and discovering the beauty of Gacka. Today, the main form of tourism in this area is a recreation and rural tourism that are extremely frequent and fishing. Tourists are able to tour the many old mills on the river of which are is still operating today. Because of strict concern for fauna in the river, fishing is allowed only in the period from 1 March to 30 September because the protection of fish populations. In some places fishing is completely prohibited (Charles canal Otočac). It is especially known for rainbow trout.  

Flora and Fauna

Gacka River is extremely rich in flora and fauna. In and around it grows 25 species of moss, algae and woody plants. With 17 aquatic animal species living brown trout (Salmo trutta), rainbow trout, pike, circulating immune complexes, grayling, brown deer cancer. Gacka is the home of men and a fish lives in deep wells and areas of eternal darkness. He recently launched a project to reduce the population of rainbow trout because it started to seriously threaten and suppress indigenous local trout.