OK, let's see if I can do my own translation and come up with something better. By the way, I found references to this song as early as 1813, and it seems to come from the area around Joachimsthal (in Brandenburg, not far from Berlin).
To start off with, "Aquarius" does not seem to be a good translation of Wasserman which refers to any male water spirit.
If you look up the term "es freit," most likely you'll end up with this song - the term doesn't seem common elsewhere. Down below, Reinhard says "freien" means to court, so I'll edit that in. I'm still not satisfied with the second-last line, "I will deprive myself of leaves and green grass."

DER WILDE WASSERMANN SONGTEXT Es freit ein wilder Wassermann Vor der Burg wohl über dem See Er freit nach königlichem Stamm, Der schönen, jungen Lilofee. Er ließ eine Brücke bau'n Vor der Burg wohl über dem See Darauf sollt' sie spazieren geht, Die schöne, junge Lilofee. Als sie auf die Brücke kam Vor der Burg wohl über dem See Der Wassermann zog sie hinab, Die schöne junge Lilofee. Drunten war sie sieben Jahr, Vor der Burg wohl über dem See Und sieben Kinder sie ihm gebar, Die schöne, junge Lilofee. Sie hörte drob' die Glocken geh'n, Vor der Burg wohl über dem See Wollt' Vater und Mutter wiederseh'n, Die schöne, junge Lilofee. Als sie aus der Kirche kam, Vor der Burg wohl über dem See Da stand der wilde Wassermann, Vor der schönen, jungen Lilofee. "Willst du hinunter geh'n mit mir? Vor der Burg wohl über dem See Deine Kinder drunten weinen nach dir, Du schöne, junge Lilofee." "Die Kinder lass uns teilen, Vor der Burg wohl über dem See Nehm' ich mir drei, nimmst Du dir drei, Ich arme, junge Lilofee." "Das siebte lass uns teilen, Vor der Burg wohl über dem See Nehm ich mir ein Bein, nimmst du dir ein Bein, Du schöne, junge Lilofee." "Eh dass ich die Kinder teilen lass, Vor der Burg wohl über dem See Scheid ich von Laub und grünem Gras, Ich arme, junge Lilofee."

THE WILD WATER SPIRIT A wild water spirit Before the castle well above the lake (over the sea?) Courted one from royal stock, The beautiful, young Lilofee. He had a bridge built Before the castle well above the lake There she was to go walking, The beautiful, young Lilofee. When she came onto the bridge Before the castle well above the lake; The water spirit pulled her down, The beautiful, young Lilofee. She was there below for seven years, Before the castle well above the lake, And seven children she bore him, The beautiful, young Lilofee. She heard the bells ringing above, Before the castle well above the lake, And she wanted to see her father and mother again, The beautiful, young Lilofee. When she came out of the church, Before the castle well above the lake, There stood the wild water spirit, Before the beautiful, young Lilofee. "Do you want you go down below with me? Before the castle well above the lake Your children are crying down below for you, You beautiful, young Lilofee. " [she said] "The children let us share, Before the castle well above the lake I will take three, and you take three, I, the poor, young Lilofee." [he said] "The seventh let us divide, Before the castle well above the lake I will take one leg, and you take one leg, You beautiful, young Lilofee." [she said] "Before I would allow the children to be divided, Before the castle well above the lake I would deprive myself (divorce myself from) of leaves and green grass, I, the poor, young Lilofee. "