Jorrit P Mesman ^1* Carolina C Barbosa ^2,3 Abigail S L Lewis ⁴ Freya Olsson ⁴ Stacy Calhoun-Grosch ⁵ Hans-Peter Grossart ^6,7 Robert Ladwig ⁸ R. Sofia La Fuente ⁹ Karla Münzner ¹⁰ Lipa G T Nkwalale ¹¹ Rachel M Pilla ¹² Keerthana Suresh ^13,14 Danielle J Wain ¹⁵

• ¹ Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
• ² Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, Colorado, United States
• ³ Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, United States
• ⁴ Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States
• ⁵ Louisiana Universities Marine Consortium, Chauvin, Louisiana, United States
• ⁶ Department of Plankton and Microbial Ecology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Berlin, Germany
• ⁷ Institute of Biochemistry and Biology, University of Potsdam, Potsdam, Brandenburg, Germany
• ⁸ Department of Ecoscience, Aarhus University, Aarhus, Central Denmark Region, Denmark
• ⁹ Department of Water and Climate, Vrije University Brussels, Brussels, Brussels, Belgium
• ¹⁰ Department of Community and Ecosystem Ecology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Berlin, Germany
• ¹¹ Department of Lake Research, Helmholtz Centre for Environmental Research, Helmholtz Association of German Research Centres (HZ), Leipzig, Lower Saxony, Germany
• ¹² Environmental Sciences Division, Oak Ridge National Laboratory (DOE), Oak Ridge, Tennessee, United States
• ¹³ International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria
• ¹⁴ Department of Physical Geography, Utrecht University, Utrecht, Netherlands, Netherlands
• ¹⁵ 7 Lakes Alliance, Belgrade Lakes, United States

Free use and redistribution of data (i.e., Open Data) increases the reproducibility, transparency, and pace of aquatic sciences research. However, barriers to both data users and data providers may limit the adoption of Open Data practices. Here, we describe common Open Data challenges faced by data users and data providers within the aquatic sciences community (i.e. oceanography, limnology, hydrology, and others). These challenges were synthesized from literature, authors’ experiences, and a broad survey of 174 data users and data providers across academia, government agencies, industry, and other sectors. Through this work, we identified seven main challenges: 1) metadata shortcomings, 2) variable data quality and reusability, 3) open data inaccessibility, 4) lack of standardization, 5) authorship and acknowledgement issues 6) lack of funding, and 7) unequal barriers around the globe. Our key recommendation is to improve resources to advance Open Data practices. This includes dedicated funds for capacity building, hiring and maintaining of skilled personnel, and robust digital infrastructures for preparation, storage, and long-term maintenance of Open Data. Further, to incentivize data sharing we reinforce the need for standardized best practices to handle data acknowledgement and citations for both data users and data providers. We also highlight and discuss regional disparities in resources and research practices within a global perspective.