The floods of April-July 1950 in the Red River of the North and Winnipeg River Basins were the largest that have occurred in several decades and caused the greatest damage that the flooded area has ever sustained. Five lives were lost in the United States, owing to causes directly connected with the floods. The dual peaks--on upper river and tributaries, one in April and the other in May--of nearly the same size and the large lake-like body of flood-water ponded between Grand Forks and Winnipeg were notable features of the flood in the Red River of the North Basin. The flood in the Winnipeg River Basin was characterized by the unusually large volume of runoff and the lateness of cresting on the Lake of the Woods. The floods were caused by a combination of causes: high antecedent soil moisture, high antecedent runoff, heavy snowfall, delayed breakup, and heavy precipitation during breakup. Mid-March snow-surveys, made in the area by hydrographers of the United States and Canadian services, showed that the snow pack north of Fargo, N. Dak., had an unusually high water content and a runoff potential increasing from west to east. A narrow band, extending from near Grand Forks, N. Dak., eastnortheastward across the basin, had a water content of 5 inches or higher. April 15 marked the beginning of rapid melting throughout the basins; most of the snow was turned into water by the end of the first melt period on April 24. A return of winter-like conditions until May 10 brought more snow and set the stage for second flood crests. The records of stage and discharge collected on the Red River of the North at Grand Forks, N. Dak., since 1882 show that the important 1897 flood slightly exceeded the 1950 flood in both stage and discharge. Records collected by the Geological Survey and Corps of Engineers on the Red River of the North show that the 1950 flood stages exceeded any previously known from just below the mouth of Turtle River to the international boundary. Records for streams tributary to the Red River of the North between Fargo and the Roseau River show, in general, that the 1950 flood events exceeded those of any known past floods. In the storage basins of the Winnipeg River, Lake of the Woods and Rainy Lake reached a stage comparable to that of 1916; and the Winnipeg River discharge at Slave Falls exceeded the highest previously recorded, maximum, which occurred in 1927. Records of floods on the Red River at Winnipeg show that the 1950 flood did not reach as high a stage as those of 1826, 1852, and 1861. The total tabulated damage to Winnipeg, the largest urban center in the area reported on, was about $20,000,000 in the city, and $12,000,000 in surrounding suburbs. The fight against flooding in Greater Winnipeg began on April 21 in the area adjacent to the municipal hospitals and was considered ended with the reopening of Norwood Bridge on June 1. About 80, 000 people were * evacuated from their homes in Greater Winnipeg during the flood, and plans were ready to evacuate a greater number had the water risen higher. This report contains records of stage and discharge for the flood period at 70 stream-gaging stations, 21 records of mean daily discharge at stream-gaging stations, 11 records of stage at river-height gages, and 7 records of storage or elevation of reservoirs or lakes. A summary table shows crest stages and discharges at 129 points for the 1950 event compared with the highest known past stages and discharges. Also included is a discussion of concurrent meteorology and of past floods on main streams and tributaries.