  With an effective Lagrangian approach, we analyze the $K^-p\to \pi^0\Sigma^0$
reaction to study the $\Lambda$ hyperon resonances by fitting the Crystal Ball
data on differential cross sections and $\Sigma^0$ polarization with the
center-of-mass energies of $1536\sim 1676$ MeV. Besides well established PDG
4-star $\Lambda$ resonances around this energy range, the $\Lambda(1600){1\over
2}^+$ resonance, listed as a 3-star resonance in PDG, is found to be definitely
needed. In addition, there is strong evidence for the existence of a new
$\Lambda({3\over 2}^+)$ resonance around 1680 MeV.
