To determine how submarine groundwater discharge (SGD) magnitudes and composition (fresh or saline/recirculated) vary in nearshore low inflow estuaries across similar to 125 km of a semiarid coastline, this study assessed three south Texas estuaries, using radon [Rn-222], radium [Ra-226 and Ra-224], and water isotopes [delta O-18 and delta D]. Mass balance models of time series Rn-222, found to be representative of total SGD in this study, revealed much higher SGD inputs to the Nueces Estuary (average [(x) over bar] Nueces, Corpus Christi and Oso Bays: 120, 83, and 44 cm.d(-1), respectively), attributed to anthropogenicallydisturbed substrates and potentially surfacing growth-faults. The lowest Rn-222-derived SGD occurred in the Upper Laguna Madre Estuary ((x) over bar: Upper Laguna Madre and Baffin Bay: 21 and 18 cm.d(-1), respectively), explained by the drier climate, lower anthropogenic disturbance, and neighboring groundwater cone of depression. Aransas Bay in the Mission Aransas Estuary received greater average annual precipitation but exhibited low total SGD rates ((x) over bar: 23 cm.d(-1)). Seasonally, average Rn-222-derived SGD rates increased following Hurricane Harvey (43 cm.d(-1) in spring to 64 cm.d(-1) in summer). In the Nueces Estuary, the overall Rn-222-derived SGDs were substantially higher than SGDs from Ra-224 and Ra-226. The closer agreement between Ra-224 and Rn-222-derived SGD and larger Ra-224 rates in the Upper Laguna Madre Estuary, Aransas Bay and Oso Bay indicate that saline/recirculated SGD contributions were significant. Values of delta O-18 and delta D confirm these types of inputs, with effects of evaporation/salinization more pronounced where recirculation was predominant and the opposite where terrestrial/Rn-222-derived SGD inputs dominate. Ra-226-derived SGDs were lower than the Ra-224 due to different behavior of the two isotopes while released into water following transport through saline and fine-grained estuarine sediments or due to wind-driven disturbances.