Although environmental DNA (eDNA) of aquatic species has been widely explored, the quantitative assessments of fish remain a challenge. eDNA approach proposed by Fukaya et al. (2021) gave a reliable abundance (the total fish population in the study area) estimates of coastal fish but was not as useful for assessing spatial distribution because of fewer eDNA samples relative to the study area. Hence, we evaluated the ability of the eDNA approach to estimate the abundance and distribution of fish in a semi-enclosed bay based on a numerical study. The evaluation was conducted as a case study on the ability of the eDNA approach according to the number of eDNA samples. Our study revealed that the eDNA approach can reliably estimate fish abundance regardless of the number of eDNA samples, if outliers of the fish density estimates are eliminated. However, when estimating spatial distribution, significant estimates were obtained only under those conditions wherein the eDNA concentration was identified in more than 70% of the study area. Therefore, it is necessary to explore other methodologies for broadly estimating eDNA concentrations with fewer samples. We have confirmed that the eDNA approach can reflect fish abundance but has limitations in estimating fish distribution. From above results, we expect our results to provide researchers with more insights into estimating the abundance and spatial distribution of fish using eDNA.