Anaerobic conditions resulting from flooding often lead to enhanced release of phosphorus (P) to overlying water. This study examined the effect of flooding and anaerobic conditions on soil P dynamics. A field ponding study using Scanterbury heavy clay soil (unamended, inorganic fertilizer- or manure-amended), and a laboratory incubation study using 12 soils (unamended or manure-amended) from Manitoba showed that P release to flood water under reduced conditions varied substantially. In the field ponding study, flooding and development of anaerobic conditions did not enhance P release into surface flood or soil pore water. In the incubation study, the response to flooding and anaerobic conditions ranged from a small decrease to a 15-fold increase in dissolved reactive P concentration (DRP) in flood water. Partial least squares analysis indicated that measures of degree of P saturation in soils can effectively predict DRP concentration changes in surface flood water under anaerobic conditions.