Switzerland has plenty of flat lakes, which is exactly what pump foiling needs. The lakes around Zürich and Zug are within an hour of each other.
Zugersee and Ägerisee
Zugersee is large and open, right by Zug city. Ägerisee is smaller, quieter and often glassy in the mornings.
Lake Zurich, Greifensee and Walensee
Lake Zurich has many access points, Greifensee is calmer and Walensee is scenic but windier in the afternoon. See all locations.