  Nonlinear behaviour of galactic dynamos is studied, allowing for magnetic
helicity removal by the galactic fountain flow. A suitable advection speed is
estimated, and a one-dimensional mean-field dynamo model with dynamic
alpha-effect is explored. It is shown that the galactic fountain flow is
efficient in removing magnetic helicity from galactic discs. This alleviates
the constraint on the galactic mean-field dynamo resulting from magnetic
helicity conservation and thereby allows the mean magnetic field to saturate at
a strength comparable to equipartition with the turbulent kinetic energy.
