Gat mort is a left tributary of the Garonne, in southwest France. It is long.
Gat mort rises in the Landes de Gascogne Regional Natural Park, in the commune of Hostens, generally drains in a north-easterly direction through the Graves wine-growing region and flows into the Garonne as a left tributary after about at the municipal boundary of Beautiran and Castres-Gironde.
Gat mort flows through the following department and towns: