 Gornje Blato-Deransko Lake is supplied by the karstic water sources of the Trebišnjica river, emerging in the proximity of the bordering hills.It is hydro-geologically connected to the Neretva river through its effluent, the Krupa river, formed out of 5 lakes (Škrka, Deranja, Jelim, Orah, Drijen) and by large portions permanently flooded, also isolated by wide groves of reedbebds and trees, thus representing the most interesting preserved area.The Krupa River is the Neretva left tributary and the main water current of Hutovo Blato, which leads the waters from Deransko Lake and Svitavsko Lake into the Neretva river.