  Quantum fluctuations in the background geometry of a black hole are shown to
affect the propagation of matter states falling into the black hole in a
foliation that corresponds to observations purely outside the horizon. A state
that starts as a Minkowski vacuum at past null infinity gets entangled with the
gravity sector, so that close to the horizon it can be represented by a
statistical ensemble of orthogonal states. We construct an operator connecting
the different states and comment on the possible physical meaning of the above
construction. The induced energy-momentum tensor of these states is computed in
the neighbourhood of the horizon, and it is found that energy-momentum
fluctuations become large in the region where the bulk of the Hawking radiation
is produced. The background spacetime as seen by an outside observer may be
drastically altered in this region, and an outside observer should see
significant interactions between the infalling matter and the outgoing Hawking
radiation. The boundary of the region of strong quantum gravitational effects
is given by a time-like hypersurface of constant Schwarzschild radius $r$ one
Planck unit away from the horizon. This boundary hypersurface is an example of
a stretched horizon.
