Petropedetes johnstoni is a species of frog in the family Petropedetidae. It is endemic to coastal Cameroon and known with certainty only from few localities. For a period, Petropedetes newtonii was considered a junior synonym of this species, leading to a much broader distribution. The two species are now considered distinct, but information on Petropedetes johnstoni sensu stricto is limited. Common name Johnston's water frog has been coined for this species.

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