Due to its location in flat, low-lying fenland near the sea, the town of Boston has always been at risk of flooding. The buttress on the south-west corner of the tower has been used since the eighteenth century for keeping a record of the heights and dates of flooding of the church by the River Witham. Flood defences were improved following the North Sea flood of 1953. The church was flooded in 1978 and again on 5 December 2013, when the North Sea flood of 2013 resulted in of water inside and outside the building.