The Paraná River streamflow is the third largest in South America and the sixth largest in the world. Thus, preserving historical Paraná hydrometric data is relevant for understanding South American and global hydroclimate changes. In this work, we rescued paper format data of daily Paraná water level observations taken uninterruptedly at Rosario City, Argentina, from January 1875 to present. The rescue consisted of the following activities: (i) imaging and digitization of paper format data, (ii) application of quality checks and homogeneity tests to the digitized water levels, and (iii) consideration of errors caused by gauge sinkings that may have occurred from 1875 to 1908. In addition, a rating curve was obtained for Rosario and it was used to convert water levels into discharges. The rescued water level observations and their associated discharge data provide the longest (last 143 years) continuous hydrometric records of the Paraná basin. The usefulness of these records was demonstrated by showing that the Paraná‐Pacific Ocean links observed after 1900 in previous studies are also evidenced in our nineteenth‐century discharge data. That is, high Paraná discharges coincided with El Niño events and with El Niño‐like states of the Interdecadal Pacific Oscillation (IPO), whereas low discharges coincided with La Niña events and with La Niña‐like IPO states.

Antico et al. (2018, https://doi.org/10.1002/2017WR020897) made available the longest hydrometric record (1875–2017) of the Paraná River of South America, one of the 10 largest rivers in the world. The oldest part of this record (1875–1883) has low accuracy because it was obtained from a hand‐drawn plot of the time series of daily water levels at Rosario City, Argentina. Here we overcame this data limitation by digitizing more accurate typewritten daily water levels observed at Rosario in 1875–1883. The digitized levels were referenced to the modern datum, subjected to quality checks, and corrected for errors caused by a gradual gauge sinking. A rating curve was used to convert water levels into discharges. Interestingly, our data capture the extreme Paraná flood associated with the very strong 1877–1878 El Niño.

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