In marine ecosystems, high-nutrient, low-chlorophyll (HNLC) regions are defined areas of the ocean where primary producer biomass is low despite high concentrations of nitrogen, phosphorus, and silica. Intensive study of these regions for the past 50 years has shown that primary production in HNLCs is limited by trace metals (iron and zinc) and to a lesser degree grazing. My lab group has been studying trace-metal limitation of primary producers in streams and found that metal limitation of primary producers is surprisingly common. Experimental nutrient and metal enrichments in 41 study streams demonstrated iron and zinc limitation in 50 and 33% of streams, respectively, which is comparable to the frequency of oceanic metal limitation. Predictive models suggest that iron and zinc limitation is more likely in streams with relatively high surface-water phosphorus concentrations (>10 µg/L). Both the experimental results and predictive models suggest that HNLC watersheds may be common and that, similar to oceanic HNLCs, low primary producer biomass is a result of metal limitation. I used datasets from the US EPA 2018-2019 Rivers and Streams assessment to identify streams in the continental US that have HNLC conditions. I then compare those data to a newly compiled dataset of metal concentrations to determine spatial overlap between HNLC and low concentrations of iron and zinc. Overall, the identification of HNLCs in freshwaters can be useful for locating areas of relatively inefficient carbon and nutrient storage in streams. Furthermore, many trace metals that can limit primary producer biomass are also of economic importance (i.e., critical minerals) and discovering the locations where metals may limit primary production can inform risk assessment as we enter an era of greater exploitation of critical minerals.