The effects of storm-drains with periodic flows on intertidal algal assemblages in 'Ewa Beach (O'ahu), Hawai'i

► Storm-drain effluent could increase the abundance of harmful algae. ► Algal assemblages were assessed in habitats near and removed from storm-drain outlets. ► Native and non-native algal abundances and richness were similar at all sites. ► Contrary to an earlier study, we found storm-drains do not affect algal assemblages. ► Findings emphasize the importance of sampling design when assessing impacts.