#MahadSatyagraha or Chavdar lake Satyagraha was a satyagraha led by Dr. Ambedkar on 20 March 1927 to allow untouchables to use water in a public lake in Mahad (currently in Raigad district), Maharashtra, India. The day (20 March) is observed as Social Empowerment day in India. 
In August 1923, Bombay Legislative Council passed a resolution that people from the depressed classes should be allowed to use places which were built and maintained by the Government.
In January 1924, Mahad which was part of the Bombay Province passed the resolution in its municipal council to enforce the act. But it was failed to implement because of the protest from the caste Hindus.
In response, Dr. Ambedkar organised a conference of ten thousand untouchables delegates at Mahad on March 20, 1927 to support the decision of Municipal Board.
Mahad municipality declared its public spaces open to untouchables and allowed Dr. Ambedkar to hold a meeting at Mahad in 1927. After the meeting, they proceeded to the 'Chavdar lake'. Dr. Ambedkar drank water from the lake and thousands of untouchables followed him.
After drinking the water by the untouchables from the lake, Caste Hindu argued that untouchables polluted the lake by taking water from it. To purify the lake, five cow products were used: milk, curds, clarified butter, cow-urine and cow-dung.
108 pots containing a mixture of these products were emptied into the lake while Brahmins recited mantras. The lake was then declared fit for caste hindu consumption.
