  LS I +61 303 is a gamma-ray binary that exhibits an outburst at GHz
frequencies each orbital cycle of $\approx$ 26.5 d and a superorbital
modulation with a period of $\approx$ 4.6 yr. We have performed a detailed
study of the low-frequency radio emission of LS I +61 303 by analysing all the
archival GMRT data at 150, 235 and 610 MHz, and conducting regular LOFAR
observations within the Radio Sky Monitor (RSM) at 150 MHz. We have detected
the source for the first time at 150 MHz, which is also the first detection of
a gamma-ray binary at such a low frequency. We have obtained the light-curves
of the source at 150, 235 and 610 MHz, all of them showing orbital modulation.
The light-curves at 235 and 610 MHz also show the existence of superorbital
variability. A comparison with contemporaneous 15-GHz data shows remarkable
differences with these light-curves. At 15 GHz we see clear outbursts, whereas
at low frequencies we see variability with wide maxima. The light-curve at 235
MHz seems to be anticorrelated with the one at 610 MHz, implying a shift of
$\sim$ 0.5 orbital phases in the maxima. We model the shifts between the maxima
at different frequencies as due to changes in the physical parameters of the
emitting region assuming either free-free absorption or synchrotron
self-absorption, obtaining expansion velocities for this region close to the
stellar wind velocity with both mechanisms.
