Human‐generated pressures are continuing to have a detrimental effect on diadromous fishes, resulting in legislative initiatives to conserve and manage these species. Field studies to inform these initiatives focus almost exclusively on larger marine, estuarine, and inland waters, neglecting the role of small coastal streams and tributaries in population recovery. As an example of the potential contribution of very small coastal streams to diadromous fish recruitment, we report here on the densities and distribution of European eel Anguilla anguilla L. and flounder Platichthys flesus (L.) in one such stream, “La Warenne,” in northeast France in October 1998 and 1999. Both species were found mainly in downstream sites in both years—flounder were captured in low numbers only, but mean CPUE values for eel were similar to the highest densities reported in the ICES WGEEL database for larger rivers of Great Britain, France and Spain in the Interreg Atlantic and North Sea areas. This small dataset illustrates that small coastal streams may represent an important, but overlooked, role in conservation strategies for European eel, and possibly flounder, indicating the need for further field studies and investigations of existing data sources to evaluate the contributions to diadromous fish recruitment of these poorly studied water courses.