i) The river Ganga originates as Bhagirathi from the Gangotri Glacier in Uttar Khasi district of Uttarakhand state. 
ii) The length of the river Ganga is about 2,525 km. 
iii) Its major tributaries from the north are Gomti, Gandak, Kosi and Ghaghara. 
iv) Its tributaries from south are Yamuna, Son and Chambal. The largest of its tributaries is the Yamuna. 
v) The Ganga river system is the largest drainage system in India. It extends over an area of 8,61,404 sq km in India. 
vi)The Ganga plain is the most densely populated place in India.  
vii) The river Ganga is known as the River Padma in Bangladesh.  
viii) The combined river of Ganga and Brahmaputra creates the World's largest delta known as Sundarbans in Bangladesh before joining the Bay of Bengal.

i) The rivers in south India are called the Peninsular rivers.
ii) Most of these rivers originate from the Western Ghats.
iii) These are seasonal rivers (non-perennial).
iv) They have a large seasonal fluctuation in volume of water as they are solely fed by rain.
v) These rivers flow in valleys with steep gradients.
vi) Based on the direction of flow, the peninsular rivers are divided into the West flowing and East flowing rivers.
East flowing rivers
a) Mahanadi:
i) The river Mahanadi (851 km) originates near Sihawa in Raipur district of Chattisgarh and flows through Odisha. Seonath, Telen, Sandur, Ib are its major tributaries.
ii) Delta of Mahanadi is one of the largest deltas in India.
b) Godavari
i) Godavari(1,465 km) is the longest of the Peninsular rivers. It is also called Vridha Ganga.
ii) It flows through the states of Telangana and Andhra Pradesh and joins the Bay of Bengal.
iii) Purna, Penganga, Pranitha, Indravathi, Tal & Salami are its major tributaries.
c) Krishna
i) The river Krishna (1,400 km) originates from a spring at a place called Mahabaleshwar in the Western Ghats of Maharashtra. Peddavagu, Musi, Koyna & Tungabhadra are its major tributaries.
ii) It is the second longest Peninsular river.
iii) It flows through Andhra Pradesh and joins the Bay of Bengal, at Hamsaladeevi.
d) Kaveri
i) The river Kaveri (800 km) originates at Tala kaveri, Kodagu hills of Karnataka.
ii) The river Kaveri is called Dhakshin Ganga or Ganga of south.
iii) The Kaveri breaks at Srirangam island with two channels, river Coleroon (Kollidam) and Kaveri.
iv)  At last, it empties in to the Bay of Bengal at Poompuhar.
West flowing rivers
a) Narmada
i) "The river Narmada (1,312 km) rises in Amarkantak Plateau in Madhya Pradesh. Burhner,Halon, Heran, Banjar, Dudhi, Shakkar, Tawa, Barna, Kolar are its tributaries.
ii) It is the largest among the west flowing rivers of Peninsular India.
iii) It forms 27 km long estuary before out falling into the Arabian sea through the Gulf of Cambay.
b) Tapti
 i) It is one of only the three rivers in Peninsular India that run from east to west- the others being the Narmada and the Mahi.
 ii) It outfalls into the Arabian Sea through the Gulf of Cambay.
 iii) Vaki, Gomai, Arunavati, Aner, Nesu, Buray, Panjhra, Bori are its tributariesaki.

Divisions of Northern Mountains are:
1) The Trans Himalayas
2) The Himalayas 
3) Eastern Himalayas or Purvanchal Hills. 
The Trans Himalayas 
i) The Trans Himalayas lies to the north of great Himalayan range. It lies in Jammu and Kashmir and Tibetan plateau. The trans Himalayas are about 40 km in its eastern and western extremities and about 225 km wide in its central part. 
ii) They contain the Tethys sediments. The rocks of this region contains fossils bearing marine sediments which are underlain by Tertiary granites. It has partly metamorphosed sediments and constitutes the core of the Himalayan axis. 
The Himalayas 
i) It constitutes the core part of northern mountains. It is an young fold mountain. It was formed by the movement of Eurasia land mass in the north and Gondwana land mass in the south. 
ii) It consists of many ranges. 
The main divisions of the Himalayas are the 
i) The Greater Himalayas (The Himadri) 
ii) The Lesser Himalayas (The Himachal) 
ii) The Outer Himalayas (The Siwalik's) 
The eastern or Purvanchal Hills 
i) These are the eastern off shoot of Himalayas. It extended in the north eastern states of India. 
ii) Most of these hills are located along the border of India and Myanmar while others are inside India. 
Importance of Himalayas: 
i) Himalayas blocks southwest monsoon winds and causes heavy rainfall to north India. 
ii) It forms a natural barrier to the sub-continent. 
iii) It is the source for many perennial rivers like Indus, Ganges, Brahmaputra, etc. 
iv) The Northern Mountains are described as the paradise of tourists due to its natural beauty. 
v) Many hill stations and pilgrim centers like Amarnath, Kedarnath, Badrinath and Vaishnavi devi temples are situated here. 
vi) It provides raw materials for many forest based industries. 
vii) It prevents cold winds blowing from the central Asia and protects India from severe cold.
viii) Himalayas are renowned for the rich bio-diversity.