Long-term annual runoff series of major rivers in the European part of Russia—the Northern Dvina, Pechora, Neva, Kuban, Don, Volga, and Terek rivers—were analyzed to identify groupings of low-water, average-water, and high-water years and to estimate the transition probabilities between these water abundance categories. The data series cover the period from the start of observations to 2015. The longest continuous record is that of the Neva River, beginning in 1859. The shortest series are those of the Pechora and Terek rivers, starting in 1925. Years with runoff exceeding the series mean by more than 5% were classified as high-water years. If the runoff was more than 5% below the mean, the year was considered low-water. Years where the runoff deviated from the mean by less than 5% (either above or below) were regarded as average-water years. A grouping within a series is defined as a continuous sequence of years belonging to the same water abundance category. The transition probability from one water abundance category to another was estimated as the ratio of the number of such transitions to the total number of years spent in the originating category. It was found that low-water spells on individual rivers last from 2 to 13 years, while high-water spells range from 2 to 10 years. For individual years, it is most likely that the same water content will continue in subsequent years.