Western Palearctic water frogs offer a unique possibility to study the genome dosage effect (GDE). There are two morphologically distinct species, Pelophylax ridibundus RR and Pelophylax lessonae LL, and their hybridogenetic hybrid Pelophylax esculentus (RL, LLR or RRL). It is supposed that RL have intermediate morphological features, LLR are more similar to P. lessonae, and RRL more similar to P. ridibundus. We tested if the morphology of the water frogs reflects the GDE, and whether it can be used in the field for determination of the genome composition. Mean values of the indices DP/CI, T/CI and F/T followed the order LL-LLR-RL-RRL-RR. After applying discriminant and canonical analyses 89% RR, 95% LL, 91% RL, 84% LLR and 52% RRL were correctly classified. Surprisingly, the L haplotype had bigger influence on morphology than the R haplotype — all hybrid genotypes were morphologically closer to P. lessonae than to P. ridibundus.