We present optical integral field observations of the H II region containing the ultraluminous X-ray source Holmberg II X-1 .
We confirm the existence of an X-ray ionized nebula as the counterpart of the source due to the detection of an extended He II \lambda 4686 region ( 21 \times 47 pc ) at the Chandra ACIS-S position .
An extended blue objects with a size of 11 \times 14 pc is coincident with the X-ray/He II \lambda 4686 region , which could indicate either a young stellar complex or a cluster .
We have derived an X-ray to optical luminosity ratio of L _ { X } / L _ { B } \geq 170 , and presumable it is L _ { X } / L _ { B } \sim 300 - 400 using the recent HST ACS data .
We find a complex velocity dispersion at the position of the ULX .
In addition , there is a radial velocity variation in the X-ray ionized region found in the He II emission of \pm 50 km s ^ { -1 } on spatial scales of 2-3 ^ { \prime \prime } .
We believe that the putative black hole not only ionizes the surrounding HII gas , but also perturbs it dynamically ( via jets or the accretion disk wind ) .
The spatial analysis of the public Chandra ACIS-S data reveals a point-like X-ray source and marginal indication of an extended component ( \ll 15 % of the total flux ) .
The XMM-Newton EPIC-PN spectrum of HoII X-1 is best fitted with an absorbed power-law in addition to either a thermal thick plasma or a thermal thin plasma or a multi-colour disk black body ( MCD ) .
In all cases , the thermal component shows relatively low temperatures ( kT \sim 0.14 - 0.22 keV ) .
Finally we discuss the optical/X-ray properties of HoII X-1 with regards to the possible nature of the source .
The existence of an X-ray ionized nebula coincident with the ULX and the soft X-ray component with a cool accretion disk favours the interpretation of an intermediate-mass black hole ( IMBH ) .
However the complex velocity behaviour at the position of the ULX indicate a dynamical influence of the black hole onto the local HII gas .