Neva Bay
Floods in St. Petersburg are usually caused by the overflow of the delta of Neva and by surging water in the eastern part of Neva Bay. They are registered when the water rises above with respect to a gauge at the Mining Institute. More than 300 floods occurred after the city was founded in 1703. Three of them were catastrophic: on 7 November 1824, when water rose to ; on 23 September 1924 when it reached , and 10 September 1777 when it rose to . However, a much larger flood of was described in 1691.