The probabilistic river stage forecast (PRSF) specifies a sequence of exceedance functions { n :n=1,...,N} such that n (h n )=P(H n >h n ), where H n is the river stage at time instance t n , and P stands for probability. The probabilistic flood forecast (PFF) should specify a sequence of exceedance functions {F n :n=1,...,N} such that F n (h)=P(Z n >h), where Z n is the maximum river stage within time interval (t 0 ,t n ], practically Z n =max{H 1 ,...,H n }. In the absence of information about the stochastic dependence structure of the process {H 1 ,...,H N }, the PFF cannot be derived from the PRSF. This article presents simple methods for calculating bounds on F n and approximations to F n using solely the marginal exceedance functions 1 ,..., n . The methods are illustrated with tutorial examples and a case study for a 1430km 2 headwater basin wherein the PRSF is for a 72-h interval discretized into 6-h steps.