  The behaviour of the space-like string tension in the high temperature phase
is studied. Data obtained in the $Z_2$ gauge model in (2+1) dimensions are
compared with predictions of a simple model of a fluctuating flux tube with
finite thickness. It is shown that in the high temperature phase contributions
coming from the fluctuations of the flux tube vanish. As a consequence we also
show that in (2+1) dimensional gauge theories the thickness of the flux tube
coincides with the inverse of the deconfinement temperature.
