  We propose three different lattice operators to measure the intrinsic width
\xi_I of the chromoelectric flux tube in pure lattice gauge theories. In order
to test these proposals we evaluate them for SU(2) and Ising LGTs in (2+1)
dimensions in the vicinity of the deconfinement transition. Using dimensional
reduction, we could perform the calculation in the effective 2d spin model
using standard S-matrix techniques. We consistently found the same result for
the three lattice operators. This result can be expressed in terms of the
finite temperature string tension as follows \xi_I=\frac{T}{2\sigma(T)} and
implies that the intrinsic width of the flux tube diverges as the deconfinement
transition is approached.
