The lake, Eim, is still held sacred by the Esthonians, and the Eim-legend is thus told by F. Thiersch, quoted also by Grimm and by Mace da Charda:- https://www.sacred-texts.com/neu/kveng/kvintro.htm

"Savage, evil men dwelt by its borders. They neither mowed the meadows which it watered, nor sowed the fields which it made fruitful, but robbed and murdered, insomuch that its clear waves grew dark with the blood of the slaughtered men. Then did the lake Him mourn, and one evening it called together all its fishes, and rose aloft with them into the air. When the robbers heard the sound, they exclaimed: 'Eim hath arisen; let us gather its fishes and treasures.' But the fishes had departed with the lake, and nothing was found on the bottom but snakes, and lizards, and toads. And Eim rose higher, and higher, and hastened through the air like a white cloud. And the hunters in the forest said: 'What bad weather is coming on!' The herdsmen said: 'What a white swan is flying above there!' For the whole night the lake hovered among the stars, and in the morning the reapers beheld it sinking. And from the swan grew a white ship, and from the ship a dark train of clouds; and a voice came from the waters: 'Get thee hence with thy harvest, for I will dwell beside thee.' Then they bade the lake welcome, if it would only bedew their fields and meadows; and it sank down and spread itself out in its home to the full limits. Then the lake made all the neighborhood fruitful, and the fields became green, and the people danced around it, so that the old men grew joyous as the youth."