Compared with small rivers and streams, the study of fish communities in large rivers remains challenging as spatial and temporal data variability can be greatly influenced by sampling strategy and operator choice. In an attempt to limit this variability, a new sampling protocol for fish communities in medium- to large-sized rivers was developed, based on point sampling by electric fishing and using standardised procedures and effort. Here, change in data quality (assemblage abundance, richness, structure and biotic index) with increasing sampling effort (from 1 to 100 sampling points) was evaluated. A total of 75 sampling points are proposed as the standard number of samples per site. Broadly, the results show that the application of 75 sampling points provides a reproducible representation of fish community structure in medium and large rivers, with little additional information provided by further sampling except under certain conditions, when 100 points are recommended to maintain data quality.