What is "wasserkirche"

The Wasserkirche ("Water Church") of Zürich, first mentioned as ecclesia Aquatica Turicensi around 1250 and as wazzirkilcha in 1256, is a church built on a small island in the Limmat, situated between the two main churches of medieval Zürich, the Grossmünster and the Fraumünster, at the Limmatquai and the Münsterbrücke.