Accumulation of suspended algae in small and mid-size rivers is usually limited by transport time, yet significant accrual of suspended algal biomass along stream networks can suggest unrealistically high growth rates of river plankton. Hydraulic storage in backwaters and benthic retention are two hypotheses that can explain this phenomenon, which we address by examining concentration-discharge (C-Q) relationships of chlorophyll and turbidity in order to infer where the suspended algae originated (proximal or distant sources) and whether they were benthic or planktonic in origin. As a proof-of-concept, we previously compared C-Q relationships upstream and downstream of a 10-km long river section with nine consecutive low-head dams within it. Upstream of the dams, storm chlorophyll hysteresis was predominantly counterclockwise during periods of low algal growth. When net autotrophic conditions preceded storms (P/R>1), a predominantly clockwise rotation indicated a more proximal benthic source of algae. During each individual storm, hysteresis downstream of the dams indicated a more proximal source of planktonic algae than at the upstream site, suggesting water column growth of riverine algae associated with the dams. Unlike chlorophyll, turbidity hysteresis showed no differences between sites. In this presentation, we apply this same C-Q approach using 2017-2022 NEON data of suspended chlorophyll, turbidity, algal taxonomy and discharge at 27 streams and rivers across the continental US. Long-term NEON data provide the opportunity to assess benthic vs. planktonic contributions to riverine algae in a broad range of stream size (2 to 300 m3s-1), channel slope (0.2 to 16.2 %) and complexity, and land use (<1 to 98% of forested cover). Preliminary results show a large variation in suspended chlorophyll concentrations across NEON sites both during baseflow (0.1 to 12 ug L-3) and stormflow (1.2 to 61.4 ug L-3), with predominantly counterclockwise and clockwise hysteresis in forested and agricultural watersheds, respectively.