There was a forest named Kamada. It did not rain there for a hundred years. The leaves dried up and the dwellers of the forest started to suffer.
The sage Atri decided that he would meditate to try and bring the rains. Atri's wife was Anasuya and she thought that she might as well perform tapasya together with her husband. Both of them started to pray to Shiva and it was very difficult to decide whose tapasya was the more difficult. Fifty-four passed and they meditated without eating or drinking anything.
Atri's meditation was finally over and he felt thirsty. He therefore asked his wife to go and fetch some water so that he might quench his thirst. While Anasuya was going to fetch the water, the river Gang appeared before her.
I am pleased with your tapasya, said Ganga. What boon do you desire?
If you are pleased with me, replied Anasuya, please make a pond here and fill the pond with your water.
Ganga obliged. Anasuya filled her water-pot from the pond and brought the water to her husband. Atri drank the water and found that it was far tastier than the water they were used to. When he asked Anasuya why this was so, she told him what happened. Both husband and wife came back to the pond. Anasuya had earned a lot of punya (store of merit) thanks to her tapasya. Ganga agreed to stay on provided Anasuya handed over to Ganga whatever punya she had acquired in one year of tapasya.
This conditon Anasuya agreed to.
Meanwhile, Shiva appeared and offered to grant Anasuya a boon. Anasuya desire the boon that Shiva would always be present in that forest. Shiva consented.
This sacred place is known as Atrishvara tirtha.