We present and analyze experimental results on the dynamics of hydrothermal waves occurring in
a laterally heated fluid layer. We argue that the large-scale modulations of the waves are governed
by a one-dimensional complex Ginzburg-Landau equation (CGLE). We determine quantitatively
all the coefficients of this amplitude equation using the localized amplitude holes observed in the
experiment, which we show to be well described as Bekki-Nozaki hole solutions of the CGLE.