Segara Anakan Cilacap waters consist of lagoon and riverine areas with mangrove forests. The mixing of inland and marine waters affects the plankton community. The research objectives were to describe plankton species richness and abundance, water quality during tides, and to analyze the relationship among them. The research method was a survey with a purposive sampling technique. Sampling was taken from five stations, four times in a dry season, on a spring tide when the maximum tidal range occurs. The water quality parameters consisted of temperature, current velocity, light penetration, pH, dissolved oxygen, free carbon dioxide, and salinity. The results showed that plankton species richness was the highest during the new moon at Station 3 near Motean and dominated by sea waters from Divisio Chrysophyta, such as Chaetoceros decipiens. The next taxa were Phylum Arthropoda, Divisio Cyanophyta, Divisio Chlorophyta, Phylum Euglenozoa, and Phylum Cnidaria. The plankton abundance was the highest during the new moon at Station 1 and dominated by sea waters from Divisio Chrysophyta, such as Chaetoceros. Water quality during the maximum tidal range in the new moon was better than the full moon at Station 1. In general, the highest plankton abundance was related to better water quality at Station 1.