The Someşul Mic basin is represented by two large streams: Someşul Cald and Belişul which unite in the Fântânele reservoir.
Someşul Cald river springs from the Piatra Grăitoare – Cârligatele region, a palm like basin with various brooks which display a remarkable flow even at their springs. The tributary streams of Someşul Cald are Seacă (Alunul Mare), Alunul Mic, Ponor and Firii (on the left side) valleys. On the right side Izbucul valley joins which collects the waters of Tomnatec and Călineasa valleys, Barna and Terpeş, Giurcuţa, Porcului, and Răchiţele valleys. It flows into Fântânele reservoir.
Beliş valley has its spring beneath Dealul Roşu hill (Alba). The main tributary streams are the Roşu, Călineasa Valley, Fulgerata, Ciurtuci and Potrii brooks. From the right side it collects Apa Caldă, Vijanul Valley, Olteanu and Monoşel brooks.
The rivers have no torrential character and do not cause damages because an important part of their streams run underground.
Fântânele reservoir is situated at 1,050 m altitude, has a surface of 826 ha and was formed as a result of damming the Someşul Cald valley downstream of its confluence with Beliş brook. It has a volume of 225-250 million m3 of water. From the storage lake, the water is deviated through a tunnel of 8.475 km, up to the turbines of the Mărişel Central Hydraulic Station. The Somes hydrographic system has a density of 0.7-0.8 km/km2, thus making this basin a real water reservoir.
The third hydrographic basin from ANP is Arieşul Mare basin.
Arieşul Mare river springs from the Vârtop pass and has as main tributary streams: Cobleş, Gârda Seacă and Popasul brooks and Albac river.
Deep waters, represented mostly by those of the endokarst (surface waters which seep into the underground through the holes in the limestone rocks), represent an important reserve supplying the surface water system.
The Plateau of Padiş – Cetăţile Ponorului represents, from a hydrological point of view, an endoreic basin (closed to the exterior), draining in the underground. The majority of waters flow into the Crişul Negru basin and a small part into the Someşul Cald basin. The plateau has a surface of 36 km2.
The Plateau of Ocoale – Scărişoara is suspended at more than 100 – 200 m above the surrounding valleys (Gârda and Ordâncuşa) and has a surface of 16 km2. The waters of this plateau reach via underground ways, emerging at the Izbucul Coteţul Dobreştilor karst spring in the Gârda basin.
