The Bolshaya is the largest river in the west of the Kamchatka Peninsula. It rises in the southern end of the
Eastern Range (Ganal Range), as does the river
Kamchatka, which flows to the east. The sources of the Bolshaya are in the Ganalsky Range. The upper part is called the
Bystraya. This is joined from the left by the
Plotnikova at from the river mouth to form the Bolshaya. The Plotnikova is long, with a catchment area of . There are many other tributaries, including the Nachilova and Goltsovka. The basin has more than one thousand lakes. There are mineral springs in the basin, including the notable Malkinskoye deposit. The mountains of the upper basin have exposed crystalline rocks, while lower down, the land is mostly covered in
peat. The banks are lined with typical Kamchatka forest, with
birch and
dwarf cedar. The river is deep and up to wide. It forms the Bolshaya Lake at its mouth. At its mouth the Bolshaya is more than wide. It flows in a generally-southwesterly direction to the coast, where it turns and flows in a south-southeast direction for about along the east side of a narrow sand-and-gravel spit before emptying into the
Sea of Okhotsk at the end of the spit. An 1870 account said that it received the river Apatcha above the town of
Bolsheretsk and then ran for to the Sea of Okhotsk. Large boats could navigate the river to within eight miles of the town. According to the
United States Hydrographic Office (1932): ==Settlements==