  We report the realization of a Bose-Einstein condensate (BEC) in the
hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling
at a relative low density suppressing the effect of avalanches. With the
suppression of avalanches a BEC containing 120.10^6 atoms is produced. The
collisional opacity can be tuned from the collisionless regime to a collisional
opacity of more than 3 by compressing the trap after condensation. In the
collisional opaque regime a significant heating of the cloud at time scales
shorter than half of the radial trap period is measured. This is direct proof
that the BEC is hydrodynamic.
