We report the results of a search for proton decay into ${e}^{+}+{\ensuremath{\pi}}^{0}$ in the 6800-ton IMB-3 water \ifmmode \check{C}\else \v{C}\fi{}erenkov detector. During 376 days of live time no events consistent with this decay were found in the 3300 ton fiducial volume. From this observation we derive a limit on the partial lifetime to be $\frac{\ensuremath{\tau}}{B}g2.4\ifmmode\times\else\texttimes\fi{}{10}^{32}$ yr (90% C.L.), which, combined with our previous result of 3.1\ifmmode\times\else\texttimes\fi{}${10}^{32}$ yr, provides a limit of 5.5\ifmmode\times\else\texttimes\fi{}${10}^{32}$ yr. The general features of the observed contained events are compatible with those expected from atmospheric neutrino interactions.
