Hydrohistorian is a free Colorado water-data resource that helps people explore water infrastructure, records and rights across the state. Its interactive map and basin pages cover 78 water districts, with information on nearly 200,000 structures and more than 2,500 gages drawn from public Colorado Division of Water Resources, HydroBase and USGS records. Users can look up ditches, wells, reservoirs, springs, gages, water providers and other features, or browse by basin and structure type.

The site brings current information together with historical context, including gage records extending back as far as 125 years. It presents details on water rights and call seniority, reservoir storage, groundwater, snow trends, drought, interstate compacts and transbasin water movement. Well-permit data is organized into approximate one-mile cells and distinguishes water-supply permits from monitoring holes, while noting that permits do not confirm that wells were drilled. Hydrohistorian also offers introductory learning material, basin summaries and an archive of historical maps, photographs and documents, helping users investigate how Colorado’s water systems work and have changed over time.