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According to chronicles1, the Volkhov river in the town of Novgorod sometimes flowed back. It happened in 1063 (5 days), 1415 (not stated for how long, but 'Volkhov and many other rivers' are said to have done that), 1461 (3 days), 1468 ('The whole summer the river Volkhov upwards flowed for four days', not sure how to read this at all), and 1525 (9 days, 'not by wind, neither by storm, but by the order of its creator the God').
1compiled in Е. П. Борисенков, В. М. Пасецкий. Тысячелетняя летопись необычайных явлений природы. 1988. (A thousand-year-long chronicle of astonishing natural phenomena).