  The ANTARES neutrino telescope is presently being built in the Mediterranean
Sea at a depth of 2500 m. The primary aim of the experiment is the detection of
high energy cosmic muon neutrinos, which are identified by the muons that are
produced in charged current interactions. These muons are detected by measuring
the Cerenkov light which they emit traversing the detector. Sometimes a high
momentum muon produces electromagnetic showers. The subject of this paper is a
method to reconstruct these showers which includes several steps: an algorithm
for the fit of the muon track parameters, preselection of detected photons
belonging to a shower, and a final fit with the preselected detected photons to
calculate the electromagnetic shower position. Finally a comparison between
data obtained with that part of the detector that is currently in operation and
simulations is presented.
