  The presence of large ionised gaseous nebulae found around some ultraluminous
X-ray sources (ULXs) provides the means to assess the mechanical and radiative
feedback of the central source, and hence constrain the efficiency and impact
on the surroundings of the super-Eddington regime powering most of these
sources. NGC 1313 X--1 is an archetypal ULX which has been reported to be
surrounded by abnormally high [O I]$\lambda$6300/H$\alpha >$ 0.1 ratios and for
which high-resolution spectroscopy in X-rays has hinted the presence of
powerful outflows. We report observations taken with the Multi-Unit
Spectroscopic Explorer of NGC 1313 X--1 in order to confirm the presence of a
nebula inflated by the winds, investigate its main sources of ionisation and
estimate the mechanical output of the source. We detect a bubble of 452
$\times$ 266\,pc in size, roughly centred around the ULX, which shows clear
evidence for shock ionisation in the outer edges. We estimate shock velocities
to be in the $\approx160-180$\,km/s range based on the line ratios. This
suggests that an average and continuous outflow power of $\sim(2-4.5) \times
10^{40}$ erg/s over a timescale of $(4.5-7.8) \times10^5$\,yr is required to
inflate the bubble. In the interior of the bubble and closer to the ULX we
detect an extended ($\sim$140\,pc) X-ray ionised region. Additionally, we
detect two supernova remnants coincidentally close to the bubble of which we
also report age and explosion energy estimates. The elongated morphology and
the kinematics of the bubble strongly suggest that the bubble is being inflated
by winds and/or jets emanating from the central source, supporting the presence
of winds found through X-ray spectroscopy. The estimated mechanical power is
comparable or higher than the X-ray luminosity of the source, providing
additional evidence in support of NGC 1313 X--1 harbouring a super-Eddington
accretor.
