Dataset: Dissolved organic matter, water quality, water isotopes, and discharge measurements of the Tapajós River, Brazil from 2016-2023

Water samples were collected near‐monthly from the Tapajós River upstream of Itaitubam Brazil (-4.3375,-56.06953). Water samples  were collected at 0.5 m depth from the river across the channel in equal spacing.  Three water samples (1 L) were collected at 0.5 m depth from the river across the channel in equal spacing and combined into a 4 L acid‐washed carboy to make a composite sample. The water was filtered through a 0.45 μm capsule filter with a peristaltic pump into acid‐rinsed high‐density polyethylene (HDPE) bottles. Filtered samples were kept cold during transport and immediately frozen upon transfer to the laboratory and kept in the dark until analysis. Samples for water isotope analysis were collected in 30 mL HDPE bottles that were filled to capacity, free of air, and stored in a dark, cool place prior to analysis.