  The discovery of superconductivity with a critical temperature of about 80~K
in La$_{3}$Ni$_{2}$O$_{7}$ single crystals under pressure has received enormous
attention. La$_{3}$Ni$_{2}$O$_{7}$ is not superconducting under ambient
pressure but exhibits a transition at $T^{\ast} \simeq 115$~K. Understanding
the electronic correlations and charge dynamics is an important step towards
the origin of superconductivity and other instabilities. Here, our optical
study shows that La$_{3}$Ni$_{2}$O$_{7}$ features strong electronic
correlations which significantly reduce the electron's kinetic energy and place
this system in the proximity of the Mott phase. The low-frequency optical
conductivity reveals two Drude components arising from multiple bands at the
Fermi level. The transition at $T^{\ast}$ removes the Drude component
exhibiting non-Fermi liquid behavior, whereas the one with Fermi-liquid
behavior is barely affected. These observations in combination with theoretical
results suggest that the Fermi surface dominated by the Ni-$d_{3z^{2}-r^{2}}$
orbital is removed due to the transition at $T^{\ast}$. Our experimental
results provide pivotal information for understanding the transition at
$T^{\ast}$ and superconductivity in La$_{3}$Ni$_{2}$O$_{7}$.
