In the town of Vicksburg, the water was 17.3m deep, topping the previous record set in 1927.
Further downstream, residents of low-lying rural areas in the state of Louisiana are preparing for the worst.
The plan is to keep flood waters away from the cities of Baton Rouge and New Orleans.
The US army corps of engineers has allowed the Mississippi to flood rural, less populated areas.
Al Jazeera's John Terrett reports from Krotz Springs.