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Little is known about the effect of tidal changes on minor flooding in most lagoonal estuaries, often due to a paucity of historical records that predate landscape changes. In this contribution, we recover and apply archival tidal range data to show that the mean tidal range in Miami, Florida, has almost doubled since 1900, from 0.32 to 0.61 m today. A likely cause is the dredging of a ∼15 m deep, 150 m wide harbor entrance channel beginning in the early 20th century, which changed northern Biscayne Bay from a choked inlet system to one with a tidal range close to coastal conditions. To investigate the implications for high‐tide flooding, we develop and validate a tidal‐inference based methodology that leverages estimates of pre‐1900 tidal range to obtain historical tidal predictions and constituents. Next, water level predictions that represent historical and modern water level variations are projected forward in time using different sea level rise scenarios. Results show that the historical increase in tidal range hastened the occurrence of present‐day flooding, and that the total integrated number of days with high‐tide floods in the 2020–2100 period will be approximately O(103) more under present day tides compared to pre‐development conditions. These results suggest that tidal change may be a previously under‐appreciated factor in the increasing prevalence of high‐tide flooding in lagoonal estuaries, and our methods open the door to improving our understanding of other heavily‐altered systems. Tabulations of historical tidal range indicate that tidal range in Miami (Florida) has approximately doubled since the 19th century, from 0.32 to 0.61 m. The likely cause appears to be the construction and dredging of the shipping channel to the Port of Miami, though historical land‐reclamation may also play a role. In this paper, we show that the increase in tidal range significantly exacerbates the number of minor flood events that are occurring throughout the Biscayne Bay region. As sea‐level rise continues, tidal changes will cause high‐tide flood impacts to be felt about a decade earlier than would have occurred under historical tidal conditions. Tidal range in the Miami downtown area almost doubled over the past century due to human‐induced bathymetric change and wetland reclamationPre‐1900 tidal predictions are estimated from historical tidal range using a tidal‐constituent inference based methodIncreased tidal range increases the probability of high‐tide flooding and shortens the time to when sea‐level rise will cause chronic flooding Tidal range in the Miami downtown area almost doubled over the past century due to human‐induced bathymetric change and wetland reclamation Pre‐1900 tidal predictions are estimated from historical tidal range using a tidal‐constituent inference based method Increased tidal range increases the probability of high‐tide flooding and shortens the time to when sea‐level rise will cause chronic flooding