Freshwater flow events are important for transporting allochthonous resources to aquatic systems. These inflows may have a role in supporting secondary productivity in rivers. We examined the change in carbon stable isotope signatures of dominant zooplankton taxa in over 9 months during a period of high rainfall in five coastal rivers. Flow was positively correlated to DOC as well as total nitrogen, filtered nitrogen and total phosphorus in some rivers. The δ13C stable isotope signatures of zooplankton showed evidence of allochthonous support for all rivers after flow events. Evidence of this support was still evident in zooplankton δ13C signatures up to 6 months after large flow events on each river. This work contributes new insights to the importance allochthonous sources of carbon in coastal flowing rivers.