William Butler Yeats included this tale in his collection "Fairy and Folk Tales of the Irish Peasantry", 1888. It was a legend of Cong, originally picked up by Samuel Lover from the old women who lived in that area.
Once upon the time there was a beautiful lady who lived near the lake, she was promised to a king's son and soon they were soon to be married; but he was murdered and thrown into the lake. She was so sad that she went out of her mind and disappeared after him. It was said the fairies took her away. In those days a White Trout was seen in the lake for the first time and people didn't know what to think about this creature who was so white. Year after year the trout was seen there and people began to think it must be a fairy so they never caught it.
One day some soldiers came to this area and laughed at the village people who believed the White Trout was a fairy; one of them decided to catch it and cook it in a frying-pan. When he put the trout in the pan it screamed as a human creature but he turned it over the other side to fry it better and ignored the screams. He kept doing that several times but there was no sign of the trout starting to cook. This villain said: "My jolly little trout, maybe you are fried enough and you are better than you look" and he put the knife into the fish. Again the trout screamed but this time it jumped out of the frying-pan on to the floor.
Suddenly a beautiful lady appeared, she was dressed in white and gold and her arm was bleeding. She said: "Look where you cut me, you villain!" she said, holding out her arm to him, "Couldn't leave me cool and comfortable in the lake and not disturb me in my duty?". The soldier was very scared and trembling all over like a dog in a wet sack, he begged for his life and asked for the lady's pardon. The lady said: "I was on duty waiting for my true love, if he comes while I am away, I'll turn you into a pinkeen, and I'll hunt you up and down until grass grows and water runs!". The soldier begged for her mercy and so the lady said: "Renounce your evil life, be a good man in future, go to your duty regularly and now take me back and put me into the lake again, where you found me."
The lady vanished and there the soldier saw the little trout, he put it in a clean plate and ran away toward the lake. He threw it into the lake and the water became red as blood for a little while and to this day there is a little red mark on the trout's side where it was cut.
The soldier became a good man and went to his duty three times a week and at last he turned hermit and he used to pray evermore for the soul of the White Trout.