Mansarovar (मानसरोवर)
“Mansarovar” (मानसरोवर) is a made two word – “manas”(मानस्) meaning “mind” and “sarovara” (सरोवर) means lake
It means a lake born out of mind or thought, Lord Brahma created Mansarovar Lake with his mind.
Dialogue between Rama and Vishwamitra
Rishi Vishwamitra told Rama about the lake Mansarovar , which are mentioned in Ramayana, Balakanda chapter 24
When Rishi Vishwamitra was taking Rama and Laxman to his ashram to kill Maricha (मारीच) and Subahu (सुबाहु), while they were crossing river Ganga near the meeting palace of river Sarayu (सरयू) and river Ganga.
Rama and Laxman heard great noises caused by water, so they asked Vishwamitra about the same.
Rama asked : –
वारिणो भिद्यमानस्य किमयं तुमुलो ध्वनि:। – “What is this sound bursting out of the waters”
Vishwamitra replied to them : –
कैलासपर्वते राम मनसा निर्मितं सर:।
ब्रह्मणा नरशार्दूल तेनेदं मानसं सर:।।1.24.8।।
“O , Rama. Brahma created out of his mind a lake on mount Kailash and so that lake is called Manasa.
तस्मात्सुस्राव सरसस्सायोध्यामुपगूहते ।
सर प्रवृत्ता सरयू: पुण्या ब्रह्मसरश्च्युता।।1.24.9।।
This river which flows from Manasa lake is known as ‘Sarayu’. It surrounds Ayodhya. This sacred river flows from that lake of Brahma.
तस्यायमतुलश्शब्दो जाह्नवीमभिवर्तते।
वारिसङ्क्षोभजो राम प्रणामं नियत:कुरु।
When Ganga approaches this river Sarayu, there is a clash of waters and this great noise is produced.
reference – https://www.valmiki.iitk.ac.in/
