Lago di Ganna is a lake at Valganna in the Province of Varese, Lombardy, Italy.

It has an area of 0,07 km² and a maximum depth of 3 m. It is part of a natural reserve.

The lake has as an underground tributary the river Margorabbia, which than becomes an emissary that flows into the near Lago di Ghirla.

It is entirely part of the frazione of Ganna and it's comprised in the Cinque Vette Park.

Between the XII and XIII centuries the benedictine monks changed the hydrography through some reclamation works.