This data package documents selected special conditions affecting the magnitude of peak flows at streamgages in Alaska. The data consist of a table of special conditions for selected peak flows and a table of data sources. This dataset verifies the basis for assignment of peak-flow qualification codes in the USGS National Water Information System (NWIS; https://doi.org/10.5066/F7P55KJN) to resolve ambiguity arising from the limited qualification codes available for special conditions. For peak flows assigned a code 3 or 9 in the NWIS peak-flow database, the special conditions forming the basis for code assignment were (1) snowmelt or (2) a sudden release of water. Subcategories of sudden releases of water included glacier dammed lake outburst, glacier and debris dammed lake outburst, sediment dammed lake outburst, mass failure/lake outburst, landslide debris dam breakup, beaver dam breakup, natural flow diversion, or subsidence from detonation. Data sources used to verify the basis for the codes included reports, online data, and USGS streamgaging notes.