  The temperature $T$ and magnetic field $H$ dependence of the resistivity
$\rho$ has been measured for La$_{0.8-y}$Sr$_{0.2}$MnO$_{3}$ (y=0 and 0.128)
films grown on (100) SrTiO$_{3}$ substrates. The low-temperature $\rho$ in the
ferromagnetic metallic region follows well $\rho (H,T)=\rho
_{0}(H)+A(H)\omega_{s}/\sinh (\hbar \omega_{s}/2k_{B}T)+B(H)T^{7/2}$ with $\rho
_{0}$ being the residual resistivity. We attribute the second and third term to
small-polaron and spin-wave scattering, respectively. Our analysis based on
these scattering mechanisms also gives the observed difference between the
metal-insulator transition temperatures of the films studied. Transport
measurements in applied magnetic field further indicate that spin-wave
scattering is a key transport mechanism at low temperatures.
