  We present a study of a peculiar nebula MF16 associated with an Ultraluminous
X-ray Source NGC6946 ULX-1. We use integral-field and long-slit spectral data
obtained with the 6-m telescope (Russia). The nebula was for a long time
considered powered by strong shocks enhancing both high-excitation and
low-excitation lines. However, kinematical properties point to rather moderate
expansion rates (V ~ 100-200 km/s). The total power of the emission-line source
exceeds by one or two orders of magnitude the power observed expansion rate can
provide, that points towards the existence of an additional source of
excitation and ionization. Using CLOUDY96.01 photoionization code we derive the
properties of the photoionizing source. Its total UV/EUV luminosity must be
about 10^{40} erg/s.
